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生殖補助医療(体外受精(IVF)や顕微授精(ICSI))における、補助孵化(アシストハッチング)

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Abstract

Background

Failure of implantation and conception may result from inability of the blastocyst to escape from its outer coat, which is known as the zona pellucida. Artificial disruption of this coat is known as assisted hatching and has been proposed as a method for improving the success of assisted conception by facilitating embryo implantation.

Objectives

To determine effects of assisted hatching (AH) of embryos derived from assisted conception on live birth and multiple pregnancy rates. 

Search methods

We searched the following databases (from their inception to 27 May 2020), with no language or date restriction: Cochrane Gynaecology and Fertility Group (CGFG) specialised register, CENTRAL, MEDLINE, Embase and PsycINFO. We checked reference lists of relevant studies and searched the trial registers.

Selection criteria

Two review authors identified and independently screened trials. We included randomised controlled trials (RCTs) of AH (mechanical, chemical, or laser disruption of the zona pellucida before embryo replacement) versus no AH that reported live birth or clinical pregnancy data.

Data collection and analysis

We used standard methodological procedures recommended by Cochrane. Two review authors independently performed quality assessments and data extraction.

Main results

We included 39 RCTs (7249 women). All reported clinical pregnancy data, including 2486 clinical pregnancies. Only 14 studies reported live birth data, with 834 live birth events. The quality of evidence ranged from very low to low. The main limitations were serious risk of bias associated with poor reporting of study methods, inconsistency, imprecision, and publication bias. Five trials are currently ongoing.

We are uncertain whether assisted hatching improved live birth rates compared to no assisted hatching (odds ratio (OR) 1.09, 95% confidence interval (CI) 0.92 to 1.29; 14 RCTs, N = 2849; I² = 20%; low‐quality evidence). This analysis suggests that if the live birth rate in women not using assisted hatching is about 28%, the rate in those using assisted hatching will be between 27% and 34%.

Analysis of multiple pregnancy rates per woman showed that in women who were randomised to AH compared with women randomised to no AH, there may have been a slight increase in multiple pregnancy rates (OR 1.38, 95% CI 1.13 to 1.68; 18 RCTs, N = 4308; I² = 48%; low‐quality evidence). This suggests that if the multiple pregnancy rate in women not using assisted hatching is about 9%, the rate in those using assisted hatching will be between 10% and 14%.

When all of the included studies (39) are pooled, the clinical pregnancy rate in women who underwent AH may improve slightly in comparison to no AH (OR 1.20, 95% CI 1.09 to 1.33; 39 RCTs, N = 7249; I² = 55%; low‐quality evidence). However, when a random‐effects model is used due to high heterogeneity, there may be little to no difference in clinical pregnancy rate (P = 0.04).

All 14 RCTs that reported live birth rates also reported clinical pregnancy rates, and analysis of these studies illustrates that AH may make little to no difference in clinical pregnancy rates when compared to no AH (OR 1.07, 95% CI 0.92 to 1.25; 14 RCTs, N = 2848; I² = 45%).

We are uncertain about whether AH affects miscarriage rates due to the quality of the evidence (OR 1.13, 95% CI 0.82 to 1.56; 17 RCTs, N = 2810; I² = 0%; very low‐quality evidence).

Authors' conclusions

This update suggests that we are uncertain of the effects of assisted hatching (AH) on live birth rates. AH may lead to increased risk of multiple pregnancy. The risks of complications associated with multiple pregnancy may be increased without evidence to demonstrate an increase in live birth rate, warranting careful consideration of the routine use of AH for couples undergoing in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI).

AH may offer a slightly increased chance of achieving a clinical pregnancy, but data quality was of low grade. We are uncertain about whether AH influences miscarriage rates.

PICOs

Population
Intervention
Comparison
Outcome

The PICO model is widely used and taught in evidence-based health care as a strategy for formulating questions and search strategies and for characterizing clinical studies or meta-analyses. PICO stands for four different potential components of a clinical question: Patient, Population or Problem; Intervention; Comparison; Outcome.

See more on using PICO in the Cochrane Handbook.

生殖補助医療(体外受精や顕微授精)における受精卵の補助孵化

レビューの論点

生殖補助医療における補助孵化(培養室で胚の孵化を手助けする操作を加えること)は、妊娠・生児出産に至る確率を高めるか、また多胎妊娠のリスクに影響を与えるか。

背景

補助孵化は、体外受精(IVF)や顕微授精(ICSI)などの生殖補助医療で用いられることがある技術である。受精卵の周りの被膜を薄くしたり、穴を開けたりする。この操作により、受精卵が子宮内膜に着床する確率が高まり、妊娠しやすくなると考えられている。

研究の特徴

7249人の女性を対象とした39件のランダム化比較試験(RCT)を対象とした。すべての研究で臨床的な妊娠が報告されていたが、生児出産について報告されたのは14件、多胎妊娠について報告されたのは18件であった。エビデンスは2020年5月までのものである。

主要な結果

補助孵化を行わない場合と比較して、補助孵化が出生率に与える影響が不確かであることが示された。補助孵化は、補助孵化を行わない場合と比較して、多胎妊娠率を若干高める可能性がある。補助孵化は、臨床的妊娠の可能性をわずかに改善する可能性がある。補助孵化の流産への影響については不明である。

今後は、生児出産と多胎妊娠を主要な結果指標として報告する研究のみを実施し、資金を提供すべきである。

エビデンスの質

エビデンスの質は低度から非常に低度であった。主な限界は、研究方法の報告不足に伴うバイアスの重大なリスク、矛盾、不正確さ、出版バイアスである。

Authors' conclusions

Implications for practice

This update suggests that we are uncertain of the effect of assisted hatching (AH) on improving live birth rate, but it may slightly improve the chance of achieving a clinical pregnancy. However this result is not robust. The increase in clinical pregnancy rate is slightly higher in women with poor prognosis including those with previously failed in vitro fertilisation (IVF)/intracytoplasmic sperm injection (ICSI). Most trials still fail to report on live birth rates. Low‐quality evidence suggests increased risk of multiple pregnancy with assisted hatching, and very low‐quality evidence suggests that AH does not increase the miscarriage rate.

Implications for research

This review once again highlights a wide range of currently unresolved issues that provide potential avenues for future research, including the need for high‐quality trials that report live births, clinical pregnancies, and adverse events (including multiple pregnancies, miscarriages, and long‐term adverse outcomes) and are powered to investigate effects in clinical subgroups.

The potential of assisted hatching in assisted conception makes it imperative that studies of high methodological quality (preferably multi‐centre trials of appropriate design, adequate power, and appropriate duration of follow‐up) are undertaken to provide these urgently needed answers; such studies should be funded only if they report the important primary outcome measures of live birth and multiple pregnancy.

Summary of findings

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Summary of findings 1. Assisted hatching compared to no assisted hatching for women undergoing assisted conception

Assisted hatching compared to no assisted hatching for women undergoing assisted conception

Patient or population: women undergoing assisted conception

Setting: clinic
Intervention: assisted hatching
Comparison: no assisted hatching

Outcomes

Anticipated absolute effects* (95% CI)

Relative effect
(95% CI)

№. of participants
(studies)

Quality of evidence
(GRADE)

Comments

Risk with no assisted hatching

Risk with assisted hatching

Live births per woman randomised

283 per 1000

301 per 1000
(267 to 338)

OR 1.09
(0.92 to 1.29)

2849
(14 RCTs)

⊕⊕⊝⊝
LOWa

Multiple pregnancy rate per woman randomised

91 per 1000

121 per 1000
(102 to 144)

OR 1.38
(1.13 to 1.68)

4308
(18 RCTs)

⊕⊕⊝⊝
LOWb

Clinical pregnancy rate per woman randomised

322 per 1000

363 per 1000
(341 to 387)

OR 1.20
(1.09 to 1.33)

7249
(39 RCTs)

⊕⊕⊝⊝
LOWb

Miscarriage rate per woman randomised

53 per 1000

60 per 1000
(44 to 81)

OR 1.13
(0.82 to 1.56)

2810
(17 RCTs)

⊕⊝⊝⊝
VERY LOWc

*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: confidence interval; OR: odds ratio; RCT: randomised controlled trial.

GRADE Working Group grades of evidence.
High quality: we are very confident that the true effect lies close to that of the estimate of the effect.
Moderate quality: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.
Low quality: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect.
Very low quality: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.

aDowngraded two levels for serious risk of bias and publication bias: in many studies, the method was unclear and information was incomplete. The main limitation was serious risk of bias associated with poor reporting of study methods.

bDowngraded two levels for serious risk of bias and for serious inconsistency.

cDowngraded three levels for serious risk of bias, serious inconsistency, and serious imprecision (only 158 events).

Background

Description of the condition

The World Health Organization estimates that one in four couples in developing countries have been found to be affected by infertility (Mascarenhas 2012). Increasing numbers of couples require treatment by the assisted conception (AC) procedures of in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI) ‐ types of assisted reproductive technology (ART). In the UK in 2018, 54,000 women had 68,727 fresh and frozen IVF cycles at Human Fertilisation and Embryology Authority (HFEA)‐licensed fertility clinics (HFEA 2020). In 2016, across 40 European countries, a total of 156,002 cycles of IVF and 407,222 cycles of ICSI were performed, with ART infants contributing to 2.9% of all births. Following IVF and ICSI, clinical pregnancy rates per transfer were 34.8% and 33.2%, respectively (ESHRE‐ European IVF monitoring consortium 2020).

The European Society of Human Reproduction and Embryology (ESHRE) reported that the most important indicator of success of ART treatment is the birth of a single healthy child (Land 2003). Following this, the Harbin Consensus Conference Workshop Group developed a modified Consolidated Standards of Reporting Trials (CONSORT) statement for infertility trials and recommended that the preferred primary outcome of all infertility trials is live birth (defined as any delivery of a live infant at ≥ 20 weeks' gestation) (Harbin Consensus Conference Workshop Group 2014).

Numerous innovations have improved assisted reproduction outcomes; these include laboratory technologies to improve fertilisation, cryopreservation techniques, blastocyst transfers to improve success (Glujovsky 2016), pre‐genetic testing (Sengupta 2012), and time lapse embryo imaging, which provides a better selection of embryos for transfer (Freour 2012).

To improve ART outcomes, a receptive endometrium in the presence of a good quality embryo is important for achieving a successful pregnancy. The quality of the transferred embryos may be affected by genetic disorders, issues with hatching (zona pellucida harding), and poor laboratory cultural conditions.

The human oocyte and early embryo is surrounded by a 13‐ to 15‐μm‐thick acellular matrix, the zona pellucida (ZP) (Bleil 1980), which is composed of glycoproteins, carbohydrates, and zona pellucida‐specific proteins (ZP1, ZP2, ZP3, ZP4) (Lefievre 2004). The zona pellucida is bi‐layered; the outer layer is thick, whereas the inner layer is thin but resilient. It is involved in sperm binding and induction of the acrosome reaction, and it promotes oocyte fusion (Gupta 2015). Following fertilisation, the zona pellucida blocks polyspermy, prevents blastomere dispersal, and helps in oviductal transport. It avoids contact with other cells (epithelial lining of the reproductive tract, leucocytes, spermatozoa, and other cells of the embryo). It is essential for maintaining the integrity of the pre‐compacted embryo. Compaction is the formation of structural junctions between blastomeres. Once compaction occurs, the zona pellucida is no longer essential (Hammadeh 2011). Zona hardening occurs naturally after fertilisation to ensure this threefold function. A combination of lysins produced by the cleaving embryo or the uterus and physical expansion then reduces the zona thickness in preparation for hatching. Zona hardening, although not readily quantifiable, may also be induced by in vitro culture and by in vivo aging (De Vos 2000).

After fertilisation, the zona maintains the three‐dimensional integrity of the uncompacted embryo for up to six days in early development, facilitates free passage of the compacted embryo through the fallopian tube into the uterus, and protects the embryo from micro‐organisms and immune cells (Bronson 1970). During embryonic development, fluid starts to accumulate between cells at the morulae stage. As the volume of fluid increases, a cavity gradually appears, forming the blastocoele. This normally happens between Days 4 and 5 in human embryos in vitro and is known as the blastocyst stage. Concurrently with the increase in fluid inside the blastocyst, the number of cells increases. This combination causes progressive enlargement of the blastocyst and its cavity, leading to progressive thinning of the ZP. Finally, the blastocyst breaks free of the ZP through a process called hatching (Hardarson 2012). This process occurs before implantation.

Human embryos resulting from controlled ovarian hyperstimulation develop more slowly in vitro compared to embryos in vivo. These embryos manifest a relatively high degree of cytogenetic abnormalities and cellular fragmentation and a reduced rate of blastocyst development, although maternal age and treatment protocols may influence rates (Hsu 1999). Cultured embryos also hatch and implant at lower rates than occurs naturally (Harlow 1982; Mercader 2001). It is unclear whether this is due to 'hardening' of the zona pellucida as a result of cross‐linking of its constituent ZP glycoproteins in an in vitro environment (Cohen 1991). With IVF and ICSI treatment, the possible combination of delayed embryo hatching and advanced endometrial development may present an unfavourable environment for implantation (Check 1999; Hsu 1999).

Description of the intervention

Artificial disruption of the zona pellucida is known as assisted hatching (AH) and was first suggested in the 1980s. It was subsequently observed in women undergoing embryo biopsy for pre‐implantation genetic diagnosis (Fehilly 1985). AH is a complementary technique to conventional ART and involves thinning or completely diminishing a small fraction of the outer coat of a fertilised egg or early embryo to encourage hatching and implantation in the receptive endometrium.

A variety of techniques have since been employed to assist embryo hatching, including chemical drilling of the ZP with acidic Tyrode’s medium, ZP thinning using acidic Tyrode’s, mechanical piercing of the ZP with a microneedle, known also as partial zona dissection (PZD), and mechanical expansion of the ZP via injected hydrostatic pressure, carving a hole in ZP via piezoelectric pulses and laser‐assisted zona drilling (Avella 2019). Regardless of the AH technique employed, it is important to distinguish whether the zona has remained unbreached (as in thinning), has been fully breached (when a hole is made chemically), or has been completely removed. This distinction may have implications for whether an embryo is able to undergo normal zona expansion and escape following AH (Blake 2001), as well as for subsequent monozygotic twinning (da Costa 2001; Menezo 2003; Schieve 2000). At present, laser AH is the most popular complementary ART technique (Hammadeh 2011)

How the intervention might work

Zona thickness appears to be influenced by a variety of factors including the woman's age (Balakier 2012), hormone profile, smoking, and cause of infertility. Increased ZP thickness correlates negatively with embryo implantation rates (Avella 2019, Loret de Mola 1997). Implantation of the embryo into the endometrium is initiated by hatching of the embryo from the surrounding ZP (Hardarson 2012). Failure of the embryonic zona pellucida to rupture following blastocyst expansion has been suggested as a possible contributing factor to failure of embryo implantation. To help embryos escape from their zona during blastocyst expansion, different types of assisted hatching have been proposed (De Vos 2000).

Many mechanisms by which AH could improve embryo implantation have been postulated. One of these mechanisms is AH overcoming the zona pellucida hardening caused by IVF and cell culture or cryopreservation. Additionally, some evidence indicates that embryos that have undergone zona manipulation for AH tend to implant one day earlier than unhatched embryos (Rink 1995). Finally, as suggested by Cohen 1992, artificial opening could enhance hormonal and metabolite exchange, as well as messaging between the embryo and the endometrium.

Why it is important to do this review

Zona manipulation of some form has been offered to women of advanced age and to those with high follicle‐stimulating hormone (FSH) levels, with high risk of zona hardening (as with in vitro oocyte maturation), and status post repeated implantation failure (Al‐Nuaim 2002). However, considerable uncertainty remains over whether AH significantly improves IVF and ICSI clinical outcomes and embryo implantation rates, or whether it is associated with negative consequences for embryo development and viability. Previous updates showed that AH results in an increase in clinical pregnancy rates when compared with no AH, but AH has failed to result in a statistically significant increase in live birth rates. However, few trials have reported on live birth rates. We hope that updating this review and incorporating more studies will provide more conclusive evidence of effects of AH on live birth rate particularly rather than only on clinical pregnancy rates, as well as its effects on other outcomes such as miscarriage and multiple pregnancy rates.

Objectives

To determine effects of assisted hatching (AH) of embryos derived from assisted conception on live birth and multiple pregnancy rates. 

Methods

Criteria for considering studies for this review

Types of studies

Published and unpublished randomised controlled trials (RCTs) were eligible for inclusion. We excluded non‐randomised studies (e.g. studies with evidence of inadequate sequence generation such as alternate days and patient numbers), as they are associated with high risk of bias. Trials were eligible for inclusion only if data could be extracted per woman and not per cycle. We excluded trials that presented results as per cycle rather than as per woman (unless it was clear in the text that per cycle and per woman were used interchangeably). We excluded cross‐over trials, as the design is not valid in this context.

Types of participants

Eligible participants were women of all nationalities and reproductive ages undergoing assisted conception by IVF or ICSI, using their own gametes and consenting to participation in a trial of AH after fertilisation.

In the subgroup analysis, poor prognosis referred to women with increased age, previous IVF failure, high FSH, or use of frozen embryos, or it was used when the primary study protocol referred to women with a poor prognosis.

Types of interventions

Trials that investigated any known method of AH after fertilisation were included. Techniques used to disrupt the zona pellucida before embryo replacement were of the following forms.

  • Mechanical.

  • Chemical.

  • Laser.

Trials in which assisted hatching took place to the following extent were eligible.

  • Breaching the zona pellucida by a hole (by laser, chemical, or mechanical means).

  • Thinning the zona pellucida (with no actual hole created).

  • Removing the entire zona pellucida.

Trials were eligible when AH was performed on fresh embryos and cryopreserved embryos following thawing and before embryo transfer, as well as on vitrified‐warmed embryos that were transferred at the cleavage stage. The effects of these interventions were compared to those of a control by which AH was not performed.

Trials directly comparing different AH methods (without including a control group with no assisted hatching performed) were excluded because the objective of this review was to determine the overall effectiveness of the technique of AH.

We excluded biopsied embryos for purposes of pre‐genetic screening (PGS)/pre‐genetic diagnosis (PGD) during assisted reproduction because this approach aims towards embryo selection ‐ not towards increased possibility of implantation per se. As assisted hatching has been proposed to improve implantation, leading to improved clinical pregnancy and live birth rates, biopsied embryos for PGS and PGD were excluded.

Types of outcome measures

Primary outcomes

  • Live birth rate per woman

  • Multiple pregnancy rate per woman

Secondary outcomes

  • Clinical pregnancy rate per woman (defined as pregnancy diagnosed by ultrasonographic visualisation of one or more gestational sacs, or definitive clinical signs of pregnancy)

  • Miscarriage rate per woman (loss of pregnancy up to 20 weeks' gestation per woman)

  • Monozygotic twinning per woman

  • Ectopic pregnancy rate per woman

  • Congenital or chromosomal abnormalities per woman

Only trials that reported at least clinical pregnancy rate per woman were included. The first version of the review included trials with implantation as an outcome; however for this update, we have removed implantation rate as an outcome. It is not possible to pool implantation, as the data are reported per embryo. We recorded live birth as an event per woman and not by the number of infants delivered because of the large number of multiple births.

Search methods for identification of studies

We searched for all published and unpublished RCTs of AH versus no AH, without language restrictions, from inception of the databases until 27 May 2020, in consultation with the Gynaecology and Fertility Group Information Specialist.

Electronic searches

We searched the following electronic databases, trial registers, and websites:

  • Cochrane Gynaecology and Fertility (CGF) Group Specialised Register of Controlled Trials, ProCite platform, searched 27 May 2020, (Appendix 1);

  • CENTRAL, via the Cochrane Register of Studies Online (CRSO), Web platform, searched 27 May 2020, (Appendix 2);

  • MEDLINE, Ovid platform, searched from 1946 to 27 May 2020, (Appendix 3);

  • Embase, Ovid platform, searched from 1980 to 27 May 2020, (Appendix 4);

  • PsycINFO, Ovid platform, searched from 1806 to 27 May 2020,(Appendix 5).

Searching other resources

  • International trial registers: the ClinicalTrials database, a service of the US National Institutes of Health (clinicaltrials.gov/ct2/home) and the World Health Organization International Trials Registry Platform search portal (www.who.int/trialsearch/Default.aspx);

  • We also handsearched the reference lists of relevant articles retrieved by the search.

Data collection and analysis

We conducted data collection and analysis in accordance with the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2019).

Selection of studies

Two review authors (LL and SH) scanned titles and abstracts from the first searches; the same methods were adopted by another review author for the second searches. Trials that appeared relevant were selected and formally assessed for inclusion independently by three review authors using an inclusion and exclusion form. We resolved disagreements through discussion. Multiple reports of the same study were collated under a single reference. We corresponded with study investigators as required to clarify study eligibility. Trials excluded at this stage are detailed in the table Characteristics of excluded studies table. We have documented the selection process with a PRISMA flow chart (Figure 1).


Study flow diagram.

Study flow diagram.

Data extraction and management

Two review authors (LL and MAA) independently extracted data from eligible studies using the Cochrane data collection form for Intervention reviews (RCTs only) (Figure 2; Figure 3). Discrepancies in data extraction were resolved by consensus during discussions with another review author (MWS or SF).


Methodological quality graph: review authors' judgements about each methodological quality item presented as percentages across all included studies.

Methodological quality graph: review authors' judgements about each methodological quality item presented as percentages across all included studies.


Methodological quality summary: review authors' judgements about each methodological quality item for each included study.

Methodological quality summary: review authors' judgements about each methodological quality item for each included study.

Assessment of risk of bias in included studies

Two review authors (LL and MAA) independently assessed the included studies for risk of bias using the Cochrane risk of bias assessment tool to assess allocation (random sequence generation and allocation concealment), blinding of participants and personnel, blinding of outcome assessors, incomplete outcome data, selective reporting, and other bias (http://handbook.cochrane.org). Disagreements were resolved by discussion or by a third review author (MWS or SF).

For each trial, it was determined whether adequate allocation concealment was described, and the trial was classed as being at low risk of bias if this was the case. If it was not the case, or if it was unclear how allocation concealment was achieved, the trial was classed as being at high risk or unclear risk, respectively. For each trial, we determined whether an acceptable method of sequence generation was described within the text (e.g. by stating that a computer‐generated randomisation list had been used). If this was the case, again the trial was classed as being at low risk in this respect. Similarly, if this was unclear, the trial was classed as having unclear risk of bias. We determined who was blinded in each trial. If participants and medical staff in the trial were blinded to allocation, the trial was at low risk. If this was not stated or if it was clear that this was not the case, the trial was again classed as having unclear risk or high risk of bias, respectively. Finally, selective reporting is an important issue in this review and is an important contributor to reporting bias, with only a minority of trials reporting on the primary outcome of live birth. Each trial that reported live birth was classed as low risk unless it did not report clinical pregnancy; in that case, it was reported as high risk. Each trial that did not report live birth was classed as high risk. Study authors were contacted if risks of bias were unclear to support the assessment

Measures of treatment effect

All outcomes were dichotomous, and results were expressed for each trial as an odds ratio (OR) with 95% confidence interval (CI); P values were calculated.

Unit of analysis issues

The primary analysis was per woman randomised. Data that did not allow valid analysis (e.g. 'per cycle' data) were not pooled. Multiple live births (e.g. twins, triplets) were counted as one live birth event.

Dealing with missing data

Attempts were made to obtain additional information on trial methods, actual original trial data, or both, by contacting the principal authors of the trials. Reminders were sent (when necessary) to study authors if no reply had been received four weeks after the initial request. Only available data were analysed, and no imputation of data was undertaken.

Assessment of heterogeneity

Consideration of the clinical and methodological characteristics of included studies was undertaken to ascertain if they were sufficiently similar for meta‐analysis to provide a clinically meaningful result. Heterogeneity between the results of different trials was examined using the I² statistic. Statistical heterogeneity was deemed significant if the P value was ≤ 0.1, that is, an indication of greater variation than would be expected by chance. I² values were also examined, and higher values (> 40%) were taken to indicate high heterogeneity (Higgins 2019).

Assessment of reporting biases

In view of the difficulty of detecting and correcting for publication bias and other reporting biases, review authors aimed to minimise their potential impact by ensuring a comprehensive search for eligible studies, and by staying alert for duplication of data. If 10 or more studies were included in an analysis, we planned to use a funnel plot to explore the possibility of small‐study effects (a tendency for estimates of the intervention effect to be more beneficial in smaller studies). Asymmetry can be found in funnel plots, especially when high heterogeneity is noted. Asymmetry detected in a funnel plot would probably be due to true heterogeneity (Stuck 1998).

Data synthesis

Studies were combined via meta‐analysis using a fixed‐effect model for AH versus no AH with RevMan 5.4 software (RevMan 2020). An increase in the odds of a particular outcome was displayed graphically in the meta‐analyses to the right of the centre‐line, and a decrease in the odds of an outcome was displayed to the left of the centre‐line.   

Subgroup analysis and investigation of heterogeneity

The following subgroup analyses were undertaken for the 2012 and 2020 updates.

  • Number of attempts: first or repeat attempt at assisted conception.

  • Mode of assisted conception: IVF or ICSI.

  • Method of assisted hatching: chemical, laser, or mechanical.

  • Prognosis of woman: good or poor.

  • Extent of AH: thinning, breaching, complete removal of zona pellucida.

  • Type of embryo: fresh or frozen embryo transfer (frozen embryo transfer included thawed cryopreserved and vitrified‐warm embryo).

Sensitivity analysis

We performed sensitivity analysis to examine the stability of results for our primary outcomes and for clinical pregnancy, in relation to:

  • adequacy of allocation concealment, by removing trials with unclear or inadequate allocation concealment; and

  • adequacy of the randomisation process, by removing trials for which the method of randomisation was unclear.

Summary of findings and assessment of the certainty of the evidence

We prepared a Summary of findings table using GRADEpro and Cochrane methods (Higgins 2011; GRADEpro GDT 2015).This table evaluated the overall quality of the body of evidence for the main review outcomes (live birth, multiple pregnancy, clinical pregnancy and miscarriage) for the main review comparison (assisted hatching versus no assisted hatching). We assessed the quality of the evidence using GRADE criteria: risk of bias, consistency of effect, imprecision, indirectness and publication bias). Judgements about evidence quality (high, moderate, low or very low) were be made by two review authors working independently (LL and MAA), with disagreements resolved by discussion. Judgements were justified, documented, and incorporated into reporting of results for each outcome. We planned to extract study data, format our comparisons in data tables and prepare a summary of findings table before writing the results and conclusions of our review.

Results

Description of studies

Results of the search

In our updated search in 2020, we identified 284 discrete records, of which 22 were examined in full text as they were potentially eligible. Twelve were excluded in 2020 as they did not meet our inclusion criteria, one was identified as a subgroup analysis of an included study (Desai 2013; Hagemann 2010), and one is awaiting classification (Elnahas A 2018); therefore eight were eligible for inclusion. The previous version of the review included 31 studies and excluded 58 studies, so altogether there are now 39 included studies and 70 excluded studies (Figure 1). Five ongoing trials are registered at http://www.clinicaltrials.gov (a service of the US National Institutes of Health) and at http://www.who.int/trialsearch/Default.aspx (The World Health Organization International Trials Registry Platform search portal) (see Characteristics of ongoing studies).

All included trials were described in published reports (full papers or abstracts). One included study was published in Spanish (González‐Ortega 2015), and one excluded study was published in Chinese (Lu 2016). In total, the studies included in our review recruited a total of 7249 women undergoing IVF or ICSI: 3688 women in the assisted hatching groups and 3561 women in the control groups.

Included studies

Study design and setting

We included a total of 39 studies, including eight new studies for this update (Abulsoud 2019; Elnahas 2017; González‐Ortega 2015; Nada 2018; Razi 2013; Safari 2017; Shi 2016; Wan 2014) (Figure 1).

The trials were carried out in 17 different countries: USA (Carter 2003; Cohen 1992; Hagemann 2010; Hurst 1998; Laffoon 1999; Lanzendorf 1998; Sagoskin 2007; Tucker 1993; Tucker 1996), Italy (Antinori 1999; Nagy 1999), Belgium (Hellebaut 1996), Turkey (Balaban 2006; Ciray 2005; Isik 2000; Isiklar 1999; Kutlu 2010), Brazil (Baruffi 2000; Petersen 2005), Australia (Ryan 1997), Germany (Jelinkova 2002), China (Fang 2010; Ge 2008; Ng 2005; Shi 2016; Wan 2014), Japan (Utsunomiya 1998), Israel (Rufas‐Sapir 2004; Stein 1995), Iran (Razi 2013; Safari 2017; Valojerdi 2010), Canada (Balakier 2009), Egypt (Abulsoud 2019; Elhelw 2005; Elnahas 2017; Nada 2018), and Mexico (González‐Ortega 2015). One European multi‐centre study involved women at IVF centres in Switzerland, France, Germany, and Spain (Germond 2004).

Participants

The age of participants ranged from 27 to 42 years (when reported). Some trials had subgroup data within them (e.g. Elnahas 2017; Ge 2008; Germond 2004; Kutlu 2010; Rufas‐Sapir 2004; Shi 2016; Stein 1995; and Tucker 1996 presented pregnancy for different age groups), whilst other studies included only women 35 years of age and older (e.g. González‐Ortega 2015; Lanzendorf 1998) or younger than 35 years old (Antinori 1999; Hurst 1998). Other studies included women of other specific age groups, for example, 38 years of age or younger (Balakier 2009; Hagemann 2010). Subgroup analysis based on age of the women has not been achievable, as studies did not categorise age groups in a universal way.

Fourteen trials included women with a poor prognosis (Abulsoud 2019; Antinori 1999; Cohen 1992; Elhelw 2005; Ge 2008; Germond 2004; González‐Ortega 2015; Jelinkova 2002; Kutlu 2010; Lanzendorf 1998; Petersen 2005; Rufas‐Sapir 2004; Stein 1995; Utsunomiya 1998). Fourteen trials included women with a good prognosis (Antinori 1999; Balakier 2009; Carter 2003; Ciray 2005; Cohen 1992; Elnahas 2017; Ge 2008; Hellebaut 1996; Hurst 1998; Kutlu 2010; Laffoon 1999; Nada 2018; Sagoskin 2007; Tucker 1993), and the remaining studies did not provide information.

Interventions

Twelve trials were repeat cycles, and eight included women undergoing their first assisted reproductive technology (ART) cycle; 19 trials did not report whether the treatment cycle was a first or repeat cycle or were mixed cycles. A total of 12 trials included women undergoing ICSI alone, 15 were IVF only, and the rest were unstated or included mixed ICSI and IVF cycles. Twenty‐eight trials involved transfer of fresh embryos exclusively, nine involved frozen or vitrified‐warmed embryos only, two used fresh and frozen embryos (Germond 2004; Ge 2008), and one study used a combination of fresh and frozen embryos (Ryan 1997).

Eleven trials employed chemical means for assisted hatching, five employed mechanical means, and 23 employed laser.

Seventeen trials utilised a breach of the zona pellucida with a hole (Antinori 1999; Cohen 1992; Germond 2004; Hagemann 2010; Hellebaut 1996; Hurst 1998; Isiklar 1999; Laffoon 1999; Lanzendorf 1998; Nagy 1999; Razi 2013; Rufas‐Sapir 2004; Ryan 1997; Sagoskin 2007; Stein 1995; Tucker 1996; Wan 2014), a further 17 utilised non‐breach thinning (Abulsoud 2019; Balaban 2006; Balakier 2009; Baruffi 2000; Ciray 2005; Elhelw 2005; Elnahas 2017; Ge 2008; Kutlu 2010; Nada 2018; Ng 2005; Petersen 2005; Safari 2017; Shi 2016; Tucker 1996; Utsunomiya 1998; Valojerdi 2010), and two performed complete zona removal (Isik 2000; Jelinkova 2002). For two studies, this was unknown (Carter 2003; González‐Ortega 2015), whilst another study used a new method of AH whereby the zona pellucida was expanding mechanically (Fang 2010). Three trials reported the thickness of the zona pellucida (in each case, choosing zona thickness > 12 µm as an inclusion criterion).

Twenty‐five trials reported the interval between AH and embryo transfer (20 trials reported less than four hours; three trials, four to eight hours; and two, longer than eight hours).

Blastocyst transfer occurred in four trials (Isik 2000; Isiklar 1999; Laffoon 1999; Wan 2014), one of which involved complete zona removal (Isik 2000).

Outcomes

Outcome measures utilised for this review were reported by varying numbers of trials.

  • 14 trials reported live birth rate.

  • 18 trials reported multiple pregnancy rate.

  • 39 trials reported clinical pregnancy rate.

  • 17 trials reported miscarriages.

  • 6 trials reported monozygotic twinning.

  • 5 trials reported ectopic pregnancy.

  • 3 trials reported congenital or chromosomal abnormalities, or both.

  • 3 trials reported embryo damage.

  • No trials reported in vitro blastocyst development post AH.

Further details about the included trials are provided in the Characteristics of included studies table and in Table 1 and Table 2.

Open in table viewer
Table 1. Mean age of participants in assisted hatching and control groups

Study

AH n, mean age (SD)

Control n, mean age (SD)

OR for clinical pregnancy

Abulsoud 2019

65, 39.2 (1.2)

65, 39.5 (1.2)

2.50 (1.14 to 5.49)

Antinori 1999: first IVF

73, 37.5

69, 36.0

1.27 (0.70 to 2.32)

Antinori 1999: repeat IVF

96, 27.5

103, 27

1.86 (0.81 to 4.25)

Balaban 2006

183, 32.4 (3.3)

183, 32.7 (3.1)

1.85 (1.19 to 2.86)

Balakier 2009

45, 32.5 (3.8)

39, 33.8 (3.2)

0.64 (0.27 to 1.55)

Baruffi 2000

51, 31.8 (3.6)

52, 31.4 (3.6)

0.74 (0.33 to 1.65)

Carter 2003

121, 34 (3.3)

82, 34 (3.2)

0.95 (0.54 to 1.67)

Ciray 2005

60, 33.1 (4.2)

30, 34.0 (3.7)

0.62 (0.26 to 1.49)

Cohen 1992: FSH < 15

69, 36.50 (3.30)

68, 36.70 (3.70)

2.11 (1.18 to 3.77)

Cohen 1992: poor prognosis

80, 36.7 (4.3)

83, 35.3 (4.2)

1.30 (0.66 to 2.55)

Cohen 1992: FSH > 15

not stated

not stated

1.30 (0.66 to 2.55)

Elhelw 2005

not stated

not stated

1.77 (0.52 to 6.01)

Elnahas 2017

80, 31.0 (4.7)

80, 31.7 (4.9)

1.58 (0.81 to 3.08)

Fang 2010

61, 32.3 (3.4)

64, 32.1 (3.6)

2.37 (1.07 to 5.28)

Ge 2008: fresh embryo

387, 31.08 (4.68)

373, 30.44 (4.15)

0.99 (0.74 to 1.32)

Ge 2008: frozen embryo

100, 31.84 (3.85)

100, 30.66 (4.42)

2.05 (0.99 to 4.22)

Germond 2004: first cycle of frozen‐thawed embryos

62, 32.8 (4.2)

53, 32.6 (3.8)

0.09 (0.01 to 0.76)

Germond 2004: poor prognosis, first cycle of fresh embryos

22, 39.3 (2.9)

21, 38.3 (3.4)

0.51 (0.10 to 2.45)

González‐Ortega 2015

154, 38.5 (2.8)

149, 37.3 (4.2)

2.71 (1.62 to 4.56)

Hagemann 2010

59, 32.1 (3.0)

62, 31.2 (3.5)

0.81 (0.37 to 1.76)

Hellebaut 1996

60, 30.9 (4.3)

60, 30.8 (3.9)

1.15 (0.55 to 2.43)

Hurst 1998

13, 30.0 (0.9)

7, 30.0 (0.8)

0.40 (0.06 to 2.89)

Isik 2000

24, 30.5 (5.2)

22, 29.1 (3.6)

2.0 (0.62 to 6.49)

Isiklar 1999

not stated

not stated

3.20 (0.91 to 11.27)

Jelinkova 2002

128, 32.3 (4.24)

129, 32.1 (3.16)

1.86 (1.12 to 3.10)

Kutlu 2010: good prognosis

73, 29.9 (2.9)

66, 28.9 (3.4)

1.06 (0.54 to 2.08)

Kutlu 2010: poor prognosis

58, 38.0 (2.3)

55, 37.4 (2.4)

1.23 (0.58 to 2.60)

Laffoon 1999

not stated

not stated

0.85 (0.28 to 2.58)

Lanzendorf 1998

41, 38.30 (0.31)

48, 38.50 (0.26)

0.90 (0.38 to 2.10)

Nada 2018

158, 31.3 (4.1)

150, 32.6 (2.4)

1.79 (1.05 to 3.07)

Nagy 1999

20, 32.0 (4.0)

20, 31.4 (3.7)

8.0 (1.44 to 44.3)

Ng 2005

80, 34.0 (range 25 to 40)

80, 34.0 (range 26 to 40)

0.81 (0.33 to 2.00)

Petersen 2005: 1 previous implantation failure

35, 34.6 (4.6)

35, 34.1 (5.3)

1.15 (0.41 to 3.19)

Petersen 2005: several previous implantation failures

40, 35.7 (3.8)

40, 35.3 (5.1)

4.11 (1.04 to 16.29)

Razi 2013

90, 32.9 (0.5)

92, 31.6 (0.4)

0.7 (0.3 to 1.6)

Rufas‐Sapir 2004

not stated

not stated

0.72 (0.38 to 1.36)

Ryan 1997

not stated

not stated

0.74 (0.35 to 1.59)

Safari 2017

30, 30.6 (5.6)

32, 29.2 (5.3)

0.58 (0.19 to 1.78)

Sagoskin 2007

118, 34.0 (3.3)

81, 34.0 (3.2)

0.94 (0.53 to1.65)

Shi 2016

82, 37.2 (2.22)

96, 36.97 (1.96)

0.65 (0.36 to 1.18)

Stein 1995

not stated

not stated

1.54 (0.67 to 3.54)

Tucker 1993

110, 34.1 (4.8)

108, 34.2 (4.1)

1.37 (0.79 to 2.35)

Tucker 1996

50, 35.3 (4.2)

50, 33.5 (4.3)

0.74 (0.35 to 1.59)

Utsunomiya 1998

not stated

not stated

1.36 (0.32 to 5.73)

Valojerdi 2010

200, 30.86 (5.82)

200, 29.85 (5.14)

0.53 (0.35 to 0.80)

Wan 2014

96, 33.1 (3.7)

102, 32.6 (3.4)

1.91 (1.08 to 3.38)

Open in table viewer
Table 2. Prognostic factors in included trials

Study ID

Balanced age between groups

Balances no. of embryos transferred

Prognosis: poor/good

FSH levels

Blastocyst transfer

Complete/partial AH

Frozen cycles

Abulsoud 2019

Yes

Yes

Poor

No data

No

Thinning

Fresh

Antinori 1999

AH mean 1.5 years older

Yes

Good and poor subgroups

No data

No

Complete hole

Not stated

Balaban 2006

Yes

Yes

Unselected

< 10

No

Thinning

Frozen

Balakier 2009

AH mean 1.3 years older

Yes

Good

< 10

No

Thinning

Fresh

Baruffi 2000

Yes

Yes

Good

No data

No

Thinning

Fresh

Carter 2003

Yes

Yes

Good

< 10

No

Not stated

Fresh

Ciray 2005

Yes

Yes

Good

< 15

No

Thinning

Fresh

Cohen 1992

Yes

Yes

Unstated

≤ 15 and > 15 subgroups

No

Complete hole

Fresh

Elhelw 2005

Yes

No data

Poor

No data

No

Thinning

Frozen

Elnahas 2017

Yes

No data

Good

No data

No

Thinning

Frozen

Fang 2010

Yes

Yes

Not stated

No data

No

Mechanical expansion

Frozen thawed

Ge 2008

Yes

Yes

Mixed

No data

No

Thinning

Fresh and frozen subgroups

Germond 2004

Yes

Yes

Mixed, in subgroups

Between 3 and 12

No

Complete hole

Fresh and frozen subgroups

González‐Ortega 2015

Yes

Yes

Poor

> 12

No

Partial

Fresh

Hagemann 2010

Mean age data given only for combined cycles 1 and 2

Yes

Under 38 years, > 2 previously failed cycles, ZP thickness > 13 micrometers

No data

No

20 micrometer diameter opening

Fresh

Hellebaut 1996

Yes

Yes

Good

No data

No

Complete hole

Fresh

Hurst 1998

Yes

Yes

Good

< 10

No

Complete hole

Fresh

Isik 2000

AH mean 1.4 years older

Yes

Unstated

< 10

Yes

Removal complete

Fresh

Isiklar 1999

No data

Yes

Unstated

No data

Yes

Complete hole

Fresh

Jelinkova 2002

Yes

Yes

Poor

No data

Yes

Removal complete

Fresh

Kutlu 2010

Yes

Yes

Good and poor subgroups

No data

No

Complete hole

Fresh

Laffoon 1999

No data

No data

Good

No data

No

Complete hole

Fresh

Lanzendorf 1998

No

Yes

Poor

No data

No

Complete hole

Fresh

Nada 2018

Yes

Yes

Good

AH 5.4 ± 1.3
No AH 6.0 ± 1.1

No

Thinning

Fresh

Nagy 1999

Yes

Yes

Unstated

No data

No

Thinning

Frozen‐thaw cycle

Ng 2005

Yes

Higher proportion of controls received 3 embryos

Unstated

< 11

No

Thinning

Frozen‐thaw cycle

Petersen 2005

Yes

Yes

Poor

No data

No

Thinning

Fresh

Razi 2013

Yes

Yes

Unstated

No data

No

Partial

Fresh

Rufas‐Sapir 2004

No data

Yes

Poor

No data

No

Complete hole

Fresh

Ryan 1997

No data

No data

Unstated

No data

No

Complete hole

Both

Safari 2017

Yes

Yes

Unstated

AH 6.4 ± 2.3

No AH 5.6 ± 2.1

No

Thinning

Frozen

Sagoskin 2007

Yes

Yes

Good

< 10

No

Hole

Fresh

Shi 2016

Yes

Yes

Advanced maternal age

< 10

No

Zona Thinning

Fresh

Stein 1995

No data

No data

Poor

No data

No

Complete hole

Fresh

Tucker 1993

Yes

Yes

Good

< 15

No

Thinning

Fresh

Tucker 1996

AH mean 1.8 years older

Yes

Not stated

No data

No

Complete hole

Fresh

Utsunomiya 1998

No data

No data

Poor

No data

No

Thinning

Fresh

Valojerdi 2010

Yes

Yes

Not stated

No data

No

Partially thinned

Vitrified‐warmed embryo

Wan 2014

Yes

Yes

Previously unsuccessful 1 fresh cycle

No data

Yes

Partial

Vitrified‐warmed embryo

AH: assisted hatching.
ET: embryo transfer.
FSH: follicle‐stimulating hormone.

Excluded studies

We excluded 72 studies from the review (see Characteristics of excluded studies). Reasons for exclusion included inadequate method of randomisation, no per woman data, inadequate reporting of clinical pregnancy, no control group, inclusion of women with donor gametes, and, in the remainder, studies were not randomised and two studies were found to be retrospective studies on close examination of the text. Conference abstracts were excluded only when further details were asked from study authors and no response was provided, and we could not utilise available data.

Risk of bias in included studies

The overall methodological quality of the included trials was considered sub‐optimal, largely due to risk of bias in the included studies. Further details of the trials' risk of bias can be found in the Characteristics of included studies table. Summaries of risk of bias for all included studies are presented in Figure 2 and Figure 3.

Allocation

Random sequence generation

All 39 trials stated that randomisation had occurred. Regarding random sequence generation, 23 studies were at low risk of this bias, 15 had unclear risk, and one was at high risk (Hagemann 2010).

Allocation concealment

Three studies were at low risk of selection bias related to allocation concealment (Abulsoud 2019; Elnahas 2017; González‐Ortega 2015), and 36 studies had unclear risk.

Blinding

Although blinding was unlikely to influence findings for the primary review outcome (live birth), eight trials employed double blinding with both the woman and the outcome assessor unaware of the allocation (Balakier 2009; Cohen 1992; Ge 2008; González‐Ortega 2015; Hagemann 2010; Lanzendorf 1998; Ng 2005; Razi 2013). In 28 studies, it is unclear if blinding was used or who was blinded (participant or assessor), and in the remaining three studies, no blinding was reported (Ciray 2005; Hellebaut 1996; Shi 2016).

Incomplete outcome data

Ideally, studies should randomise women on the day of assessment of embryos for suitability for embryo transfer. Two studies we assessed as high risk related to incomplete outcome data (Nada 2018; Safari 2017). One excluded participants after randomisation due to cycle cancellation but gave no reason for why cycles were cancelled, and one randomised 32 participants into each trial arm but reported outcomes for only 30 participants. A total of 16 studies were at low risk of bias related to incomplete outcome data, and 21 studies had unclear risk.

Selective reporting

All pre‐specified outcomes were reported within the outcomes of all studies. Many studies did not report live birth, multiple pregnancy, or miscarriage outcomes.

Other potential sources of bias

Age groups were matched in trials with similar means in the AH and control groups.

Thirty‐two trials were reported as full published papers. Seven trials were published in conference abstract form only (Antinori 1999; Carter 2003; Elhelw 2005; Laffoon 1999; Rufas‐Sapir 2004; Ryan 1997; Utsunomiya 1998).

No funding bias or any other conflicts of interests were noted in the included studies.

Effects of interventions

See: Summary of findings 1 Assisted hatching compared to no assisted hatching for women undergoing assisted conception

Assisted hatching compared to no assisted hatching

Primary outcomes
Live birth per woman

Only 14 of the 39 trials reported live birth rate. We are uncertain of the effect of AH on live birth rate when compared to no AH (odds ratio (OR) 1.09, 95% confidence interval (CI) 0.92 to 1.29; 14 RCTs, N = 2849; I² = 20%; low‐quality evidence; Analysis 1.1; Figure 4).


Forest plot of comparison: 1 Live birth rate, outcome: 1.1 Live birth per woman randomised.

Forest plot of comparison: 1 Live birth rate, outcome: 1.1 Live birth per woman randomised.

Subgroup analysis

  • Number of attempts ‐ first or repeat attempt at ART: no evidence indicates that the effect of assisted hatching differed between those undergoing their first or subsequent attempts (P = 0.23). We are uncertain of the effect of AH on the live birth rate in women in their first attempt at ART (OR 0.78, 95% CI 0.48 to 1.28; 3 RCTs, n = 380; I² = 15%) or in subsequent attempts at ART (OR 1.40, 95% CI 0.62 to 3.13; 1 RCT only) when compared to no AH (Analysis 1.2)

  • Mode of conception ‐ assisted conception procedure (IVF/ICSI): no evidence shows that the effect of assisted hatching differed between those undergoing IVF and those undergoing ICSI (P = 0.20). For couples undergoing ICSI, AH may improve slightly the live birth rate when compared to no AH (OR 1.54, 95% CI 1.02 to 2.33; 3 RCTs, n = 640; I² = 0%). For couples undergoing IVF, there may be little to no difference in live birth rate with AH compared to no AH (OR 1.00, 95% CI 0.60 to 1.68; 3 RCTs, n = 241; I² = 58%) (Analysis 1.3)

  • Method of assisted hatching: no evidence suggests that the effect of assisted hatching differed between chemical and laser methods (P = 0.80). We are uncertain of the effect of chemical AH or laser AH on live birth rate when compared to no AH (OR 1.13, 95% CI 0.74 to 1.74; 4 RCTs, n = 366; I² = 5%; and OR 1.07, 95% CI 0.89 to 1.28; 10 RCTs, n = 2473; I² = 24%, respectively). None of the trials that employed mechanical forms of AH reported on live births (Analysis 1.4)

  • Prognosis: no evidence shows that the effect of assisted hatching differed between women in poor prognosis groups and women in good prognosis groups (P = 0.12). We are uncertain of the effect of AH on live birth rate in women with a good prognosis compared with no AH (OR 1.03, 95% CI 0.83 to 1.28; 6 RCTs, n = 1495; I² = 23%) and in women with a poor prognosis who underwent AH compared to no AH (OR 1.46, 95% CI 0.99 to 2.15; 4 RCTs, n = 576; I² = 0%) (Analysis 1.5)

  • Extent of zona manipulation: no evidence indicates that the effect of assisted hatching differed between thinning of zona and breaching the zona with a hole (P = 0.64). We are uncertain of the effect of AH with thinning of the zona pellucida on live birth rate compared with no AH and AH with breech of the zona pellucida on live birth rate compared with no AH (OR 1.06, 95% CI 0.86 to 1.30; 6 RCTs; I² = 31%; and OR 1.15, 95% CI 0.87 to 1.51; 8 RCTs, n = 1107; I² = 21%, respectively) (Analysis 1.6)

  • Type of embryo ‐ fresh or frozen embryo: no evidence shows that the effect of assisted hatching differed between fresh and frozen embryos (P = 0.35). We are uncertain of the effect of AH on live birth rate in women who had fresh embryo transfer compared with the no AH group (OR 1.16, 95% CI 0.94 to 1.44; 11 RCTs, N = 1669; I² = 16%). Only one study reported use of frozen embryos (Safari 2017), and two studies reported use of fresh and frozen embryos (Ge 2008; Germond 2004)

Sensitivity analysis

Other analyses

We used a funnel plot to assess publication bias and small‐study effects. The funnel plot shows only some mild asymmetry (Figure 5). The funnel plot is likely to be detecting small‐study effects.


Funnel plot of comparison: 1 Live birth: assisted hatching compared with no assisted hatching, outcome: 1.1 Live birth per woman randomised.

Funnel plot of comparison: 1 Live birth: assisted hatching compared with no assisted hatching, outcome: 1.1 Live birth per woman randomised.

Multiple pregnancy per woman

Eighteen of the 39 trials reported on multiple pregnancy. AH may lead to a higher multiple pregnancy rate compared to no AH (OR 1.38, 95% CI 1.13 to 1.68; 18 RCTs, n = 4308; I² = 48%; low‐quality evidence; Analysis 2.1; Figure 6).


Forest plot of comparison: 4 Multiple pregnancy rate, outcome: 4.1 Multiple pregnancy rate per woman randomised.

Forest plot of comparison: 4 Multiple pregnancy rate, outcome: 4.1 Multiple pregnancy rate per woman randomised.

Subgroup analysis

  • Number of attempts ‐ first attempt or repeat attempt at ART: no evidence indicates that the effect of AH differed between those undergoing their first attempt and those undergoing subsequent attempts (P = 0.28). We are uncertain of the effect of AH on the multiple pregnancy rate in women who underwent AH compared with no AH in their first attempt at ART (OR 0.73, 95% CI 0.31 to 1.72; 4 RCTs, n = 654; I² = 0%) or in subsequent attempts at ART (OR 1.25, 95% CI 0.80 to 1.94; 5 RCTs, n = 1068; I² = 25%) (Analysis 2.2)

  • Mode of conception‐ assisted conception procedure (IVF/ICSI): no evidence shows that the effect of AH differed between those undergoing IVF and those undergoing ICSI treatment (P = 0.21). For couples undergoing ICSI, AH may lead to slightly higher multiple pregnancy rates when compared to no AH (OR 3.09, 95% CI 1.57 to 6.08; 3 RCTs, n = 573; I² = 52%). For couples undergoing IVF, AH may lead to slightly higher multiple pregnancy rates when compared to no AH (OR 1.87, 95% CI 1.28 to 2.72; 6 RCTs, n = 1126; I² = 36%) (Analysis 2.3)

  • Method of assisted hatching: evidence suggests that the effect of AH differed between chemical, laser, and mechanical methods (P = 0.08). We are uncertain of the effect of chemical AH on the multiple pregnancy rate when compared to no AH (OR 1.55, 95% CI 0.98 to 2.47; 4 RCTs, n = 534; I² = 10%). Both laser and mechanical AH may lead to a slightly higher multiple pregnancy rate when compared to no AH (OR 1.29, 95% CI 1.03 to 1.61; 4 RCTs, n = 534; I² = 50%; and OR 8.33, 95% CI 1.56‐44.64; 1 RCT only, n = 44, respectively) (Analysis 2.4)

  • Prognosis: some evidence suggests that the effect of AH differed between women in poor prognosis groups and women in good prognosis groups (P = 0.02). We are uncertain of the effect of AH on the multiple pregnancy rate in women with a good prognosis compared with no AH (OR 1.08, 95% CI 0.81 to 1.44; 6 RCTs, n = 1569; I² = 0%). In women with a poor prognosis, AH may lead to a slightly higher multiple pregnancy rate when compared to no AH (OR 1.95, 95% CI 1.27 to 3.00; 6 RCTs, n = 1186; I² = 0%) (Analysis 2.5)

  • Extent of zona manipulation: no evidence indicates that the effect of AH differed between thinning of zona and breaching of zona with a hole (P = 0.65). AH may lead to a slightly higher multiple pregnancy rate in women who had assisted hatching with thinning of the zona pellucida compared with no AH (OR 1.34, 95% CI 1.02 to 1.76; 6 RCTs, n = 2148; I² = 71%) and assisted hatching with breech of the zona pellucida by a hole only compared with no AH (OR 1.51, 95% CI 1.08 to 2.11; 9 RCTs, n = 1629; I² = 35%). Only one study reported complete removal of the zona pellucida (Isik 2000) (Analysis 2.6)

  • Type of embryo ‐ fresh or frozen embryo: no evidence suggests that the effect of assisted hatching differed between fresh and frozen embryos (P = 0.46). We are uncertain of the affect of AH on the multiple pregnancy rate in women who had fresh embryo transfer compared with no AH (OR 1.30, 95% CI 0.98 to 1.73; 13 RCTs, n = 2264; I² = 0%) and in women who had frozen embryo transfer compared with no AH (OR 1.60, 95% CI 1.00 to 2.55; 3 RCTs, n = 926; I² = 88%) (Analysis 2.7)

  • Multiple pregnancy per pregnancy: overall, AH may lead to a higher multiple pregnancy rate compared to control (OR 1.37, 95% CI 1.09 to 1.72; 17 trials, n = 1598; I² = 25%) (Analysis 2.8)

Sensitivity analysis

Secondary outcomes
Clinical pregnancy rate per woman

Thirty‐nine trials reported clinical pregnancy data. AH may improve slightly the clinical pregnancy rate compared to no AH (OR 1.20, 95% CI 1.09 to 1.33; I² = 55%; low‐quality evidence; Analysis 3.1; Figure 7). Furthemore, the forest plots show high heterogeneity. When a random‐effects model is used, there may be little to no difference in clinical pregnancy rate among women who underwent AH compared with those given control (P = 0.04).


Forest plot of comparison: 2 Clinical pregnancy, outcome: 2.1 Clinical pregnancy rate per woman randomised.

Forest plot of comparison: 2 Clinical pregnancy, outcome: 2.1 Clinical pregnancy rate per woman randomised.

Among the 14 trials reporting both clinical pregnancy and live births, analysis demonstrated that we are uncertain of the effect of AH on clinical pregnancy rate in women who underwent AH compared with those given the control (OR 1.07, 95% CI 0.92 to 1.25; I² = 45%) (Analysis 4.1).

Subgroup analysis

  • Number of attempts ‐ first or repeat attempt at ART: some evidence suggests that the effect of AH differed between those undergoing their first attempt and those undergoing subsequent attempts (P < 0.00001; fixed model). When the random‐effects model is used, the effect is less pronounced (P = 0.0002). With the fixed‐effect model, there may be a slight decrease in the clinical pregnancy rate among women who underwent AH compared with no AH in their first attempt at ART (OR 0.74, 95% CI 0.56 to 0.98; 8 RCTs, n = 1010 women; I² = 9%). There may be slight improvement in clinical pregnancy rate among women who underwent AH compared to no AH in women undergoing repeat attempts at ART (OR 1.65, 95% CI 1.34 to 2.04; 11 RCTs, n = 1798; I² = 38%) (Analysis 3.2)

  • Mode of conception ‐ assisted conception procedure (IVF/ICSI): no evidence shows that the effect of AH differed between those undergoing IVF and those undergoing ICSI treatment (P = 0.62). For couples undergoing ICSI, AH may improve slightly the clinical pregnancy rate when compared to no AH (OR 1.40, 95% CI 1.14 to 1.71; 11 RCTs; n = 1825; I² = 30%). For couples undergoing IVF, AH may improve slightly the clinical pregnancy rate when compared to no AH (OR 1.31, 95% CI 1.10 to 1.55; 15 RCTs, n = 2460; I² = 28%) (Analysis 3.3)

  • Method of assisted hatching: no evidence indicates that the effect of AH differed between laser, chemical, and mechanical methods (P = 0.48) (Analysis 3.4). Chemical AH may improve slightly the clinical pregnancy rate when compared to no AH (OR 1.33, 95% CI 1.08 to 1.64; 11 RCTs, n = 1536; I² = 0%). Laser AH may improve slightly the clinical pregnancy rate when compared to no AH (OR 1.15, 95% CI 1.03 to 1.30; 23 RCTs, n = 5127; I² = 67%). We are uncertain of the effect of mechanical AH on the clinical pregnancy rate when compared to control (OR 1.30, 95% CI 0.89 to 1.88; 5 RCTs, n = 586; I² = 51%)

  • Prognosis: some evidence suggests that the effect of AH differed between women in poor prognosis groups and women in good prognosis groups (P = 0.0009; fixed‐effect model). When a random‐effects model is used, the effect is less pronounced (P = 0.005) than with the fixed‐effect model. In women with a good prognosis, we are uncertain of the effect of AH on the clinical pregnancy rate when compared with no AH (OR 1.10, 95% CI 0.94 to 1.29; 14 RCTs, n = 2721; I² = 0%). In women with a poor prognosis, AH may improve slightly the clinical pregnancy rate when compared with no AH (OR 1.68, 95% CI 1.38 to 2.04; 14 RCTs, n = 2108; I² = 25%) (Analysis 3.5)

  • Extent of zona manipulation: some evidence shows that the effect of AH differed depending upon the extent of assisted hatching (P = 0.04). In women who had AH with thinning of the zona pellucida, we are uncertain of the effect on the clinical pregnancy rate when compared to no AH (OR 1.10, 95% CI 0.96 to 1.26; 17 RCTs, n = 3774; I² = 57%). In women who had AH with breech of the zona pellucida by a hole only, we are uncertain of the effect of AH on clinical pregnancy rate when compared with control (OR 1.17, 95% CI 0.98 to 1.39; 17 RCTs, n = 2543; I² = 46%). Only two studies used AH with complete removal of the zona pellucida (Isik 2000; Jelinkova 2002), and only one study used AH with expansion of the zona pellucida (Fang 2010) (Analysis 3.6)

  • Type of embryos ‐ fresh or frozen embryo: in fresh embryo groups: no evidence indicates that the effect of AH differed between fresh and frozen embryos (P = 0.58). AH may improve slightly the clinical pregnancy rate in women who had fresh embryo transfer when compared with no AH (OR 1.23, 95% CI 1.10 to 1.38; 30 RCTs, n = 5349; I² = 41%). We are uncertain of the effect of AH on the clinical pregnancy rate in women who had frozen embryo transfer when compared to no AH (OR 1.15, 95% CI 0.93 to 1.42; 10 RCTs, n = 1700; I² = 76%) (Analysis 3.7)

Sensitivity analysis

  • Allocation concealment: limiting the analysis to trials that reported allocation concealment left only three trials (Abulsoud 2019; Elnahas 2017; González‐Ortega 2015). Analysis of the data from these trials suggests that there was improvement in the clinical pregnancy rate in the AH group when compared to the no AH group (OR 2.28, 95% CI 1.59 to 3.27; n = 593; I² = 0%)

  • Method of randomisation: 23 trials stated an acceptable method of randomisation. Analysis of the data from these trials suggests that there was improvement in the clinical pregnancy rate in the AH group compared to the no AH group (OR 1.16, 95% CI 1.03 to 1.30; n = 5050; I² = 63%)

Other analyses

We used a funnel plot to assess publication bias and small‐study effects. The funnel plots are symmetrical (Figure 8Figure 9).


Funnel plot of comparison: 3 Clinical pregnancy: assisted hatching compared with no assisted hatching, outcome: 3.1 Clinical pregnancy rate per woman randomised.

Funnel plot of comparison: 3 Clinical pregnancy: assisted hatching compared with no assisted hatching, outcome: 3.1 Clinical pregnancy rate per woman randomised.


Funnel plot of comparison: 4 Clinical pregnancies in trials that reported live births: assisted hatching compared with no assisted hatching, outcome: 4.1 Clinical pregnancies in trials reporting live births.

Funnel plot of comparison: 4 Clinical pregnancies in trials that reported live births: assisted hatching compared with no assisted hatching, outcome: 4.1 Clinical pregnancies in trials reporting live births.

Miscarriage per woman

Seventeen (17) trials reported miscarriage rates, accounting for 2810 women. Due to the quality of the evidence, we are uncertain about the difference in miscarriage rate among women who underwent AH compared with those who underwent no AH (OR 1.13, 95% CI 0.82 to 1.56; 17 RCTs, n = 2810; I² = 0%; very low‐quality evidence; Figure 10; Analysis 5.1).


Forest plot of comparison: 3 Miscarriage rate, outcome: 3.1 Miscarriage per woman randomised.

Forest plot of comparison: 3 Miscarriage rate, outcome: 3.1 Miscarriage per woman randomised.

Subgroup analysis

  • Number of attempts ‐ first or repeat attempt at ART: no evidence indicates that the effect of AH differed between those undergoing their first or subsequent attempts (P = 0.18) (Analysis 5.2)

  • Mode of conception ‐ assisted conception procedure (IVF/ICSI): no evidence shows that the effect of AH differed between those undergoing IVF and those undergoing ICSI treatment (P = 0.90) (Analysis 5.3)

  • Method of assisted hatching: no evidence suggests that the effect of AH differed between methods of AH (P = 1.00) (Analysis 5.4)

  • Prognosis: no evidence indicates that the effect of AH differed between women in poor prognosis groups and women in good prognosis groups (P = 0.73) (Analysis 5.5)

Monozygotic twinning

Six trials reported data on monozygotic twinning (Figure 11). Hurst 1998 reported two monozygotic twins from three pregnancies in the AH group and none in the control group (0 from three pregnancies). Hagemann 2010 reported one case of monozygotic twins in the AH group also. Balakier 2009, Isik 2000, Jelinkova 2002, Lanzendorf 1998, and Ng 2005 reported absence of monozygotic twins in either group. There was an overall rate of 0.8% for the AH group and 0% for the control group (Analysis 6.1).


Forest plot of comparison: 5 Monozygotic twinning rate, outcome: 5.1 Monozygotic twinning per woman randomised.

Forest plot of comparison: 5 Monozygotic twinning rate, outcome: 5.1 Monozygotic twinning per woman randomised.

Ectopic pregnancy

Five trials reported ectopic pregnancy data. Lanzendorf 1998 reported one ectopic pregnancy in the control group and none in the AH group. Hagemann 2010, Hellebaut 1996, and Hurst 1998 reported absence of ectopic pregnancies. Shi 2016 reported one ectopic pregnancy each in the AH and control groups.

Congenital or chromosomal abnormalities

Two trials reported absence of congenital or chromosomal abnormalities (Hurst 1998; Lanzendorf 1998), and two trials reported fetal abnormalities in both AH and control groups (Hagemann 2010; Razi 2013).

Failure to transfer any embryos per woman

No trials reported data on this outcome.

Embryo damage

Three trials reported absence of embryo damage (Hurst 1998; Lanzendorf 1998; Stein 1995).

In vitro blastocyst development

No trials reported data on in vitro blastocyst development.

No further analyses were performed because of the paucity of data on these secondary outcomes.

Assessment of reporting bias

We produced funnel plots for the outcomes of live birth (Figure 5) and clinical pregnancy (Figure 8; Figure 9), and we did not find any strong suggestion of publication bias.

Discussion

Summary of main results

Live birth

For this update, the primary outcome remained live birth rate. However only 14 of the 39 studies reported this outcome, representing 39% of all women randomised in the studies.

We are uncertain of the effects of assisted hatching (AH) on live birth rates when compared to no AH (summary of findings Table 1). It is disappointing that the conclusions of this review are still limited by the paucity of available data since publication of the first Cochrane Review on this topic. Researchers still are not publishing the most important and sought after statistic on the impact of AH on assisted conception, namely, the 'live birth (take home baby rate)'. This reflects the gap that continues to exist between the practice of assisted conception and clinical obstetrics, with the absence of a central database of patient records that would facilitate follow‐up of these women by authorised agencies. Moving forward, we hope that with publication of the modified CONSORT statement to improve reporting of fertility trials, the primary outcome measure of all fertility trials in the future will be live birth (Harbin Consensus Conference Workshop Group 2014). Reported live birth data in one‐third of all studies suggest haste on the part of study authors to disseminate data limited to short‐term outcomes, and for all intents and purposes, these data are incomplete.

Multiple pregnancy

AH may lead to a higher multiple pregnancy rate compared to no AH; furthermore, an increase in multiple pregnancies per clinical pregnancy has been noted (37% increase in odds ratio (OR)). Given this significance in combination with uncertainty about any evidence of an increase in success at achieving live birth with AH, we may need to consider the overall risks versus benefits of this technique.

Only half of the studies that report multiple pregnancy rates also report live birth data. This is unfortunate as it limits interpretation of results, given this high multiple pregnancy rate, because as many as 5% of multiple pregnancies are lost at between 20 and 40 weeks' gestation. In addition, many studies were transferring two to four embryos, although the numbers transferred were balanced between groups. The increase in multiple pregnancies can be attributed to an increase in implantation rates resulting in higher pregnancy rates or monozygotic twinning, or both, with AH. This must be taken into consideration in planning this procedure.

It is likely that reducing to one the number of embryos transferred will not completely eliminate monozygotic twinning. Implantation rate was not considered as an outcome in this update for two reasons. Pooling of embryo implantation data for meta‐analysis is statistically problematic. Implantation is traditionally expressed 'per embryo transferred', without regard for the number of women. However, more than one embryo is normally transferred per woman, resulting in an embryo clustering effect and necessitating more advanced analysis to render the results meaningful. A statistically valid and easier approach is to express implantation 'per woman randomised'. This also confers the advantage of being more useful in aiding understanding of resulting live births. This approach requires, however, that the number of women with at least one gestation sac is reported, which is not the case in practice.

Clinical pregnancy

All 39 included trials reported on clinical pregnancy. Similar to the previous update (in 2012), this update suggests that overall, AH may slightly improve the chance of achieving a clinical pregnancy, but these results are less reliable because of high risk of bias and dependence upon the statistical model. Subgroup analysis supports these results.

When analysis of clinical pregnancy rate was restricted to those trials that went on to report live birth, the clinical pregnancy result showed little to no difference in effect between AH and control groups.

Miscarriage

We are uncertain of the effect of AH on miscarriage rates when compared to controls.

Other outcomes

The impact of AH on ectopic pregnancy, congenital and chromosomal abnormalities, blastocyst formation, and embryo damage could unfortunately not be determined by this review because of the paucity of available data. This is disappointing as it leaves many unanswered questions about perceived risks of the procedure, from embryo damage to chromosomal and congenital abnormalities.

Overall completeness and applicability of evidence

A large number of trials were incorporated into this review, involving a large sample size. The results of 7249 women in 39 trials are included in this review, leading to a low to very low level of evidence. Failure of many trials to report on primary outcomes (live birth, multiple pregnancy) and variable levels of reporting on other outcomes allow potential bias to be introduced into the analysis. This calls for standardised outcome reporting for future assisted conception trials as discussed.

Quality of the evidence

The quality of the evidence is low to very low. The main limitations are serious risk of bias associated with poor reporting of study methods, inconsistency, imprecision, and publication bias (summary of findings Table 1).

Potential biases in the review process

Three review authors (LL, SH, and MAA) with varying levels of expertise undertook the search process several times to minimise the risk of bias introduced by review authors; they had no conflicts of interest.

We were unable to get responses from authors of various studies when abstracts were published and we had requested relevant or additional data. These studies could potentially have been included in the review.

Agreements and disagreements with other studies or reviews

Overall, the addition of eight new trials to this update has not changed the findings regarding live birth that were reported in previous reviews, namely, that no current evidence suggests that AH increases the chances of a live birth.

Clinical pregnancy rate may improve slightly in women undergoing AH, but these results are not reliable and robust.

Three recent non‐Cochrane systematic reviews have been published (He 2018; Li 2016; Zeng 2018). Li 2016 used random‐effects models for their meta‐analysis. They suggested that there is an increase in clinical pregnancy and multiple pregnancy rates with AH when compared to control. We agree with these findings generally, but Li 2016 did not present clear assessment of the quality and robustness of evidence related to these outcome improvements. Review authors suggested there was no improvement in live birth rates and no difference in miscarriage rates between AH and control groups. Li 2016 reported clinical pregnancy in 36 RCTs; however, this present Cochrane Review included 39 RCTs reporting clinical pregnancy (some different from the studies included by Li 2016), One RCT ‐ Urman 2002 ‐ which is reported in Li 2016 ‐ was excluded from the previous published Cochrane Review due to inadequate methods of allocation. He 2018 published a systematic review about AH that focused on a population of women older than 35 years of age. These review authors similarly demonstrated no increase in live birth rate or miscarriage rate with AH compared to control. Conversely, they demonstrated no increase in multiple pregnancy and no improvement in clinical pregnancy rate with AH compared to control. Our Cochrane Review did not specifically look at this subgroup, but this population was incorporated into our poor prognosis subgroup. Our data for the poor prognosis subgroup suggest that AH may improve slightly clinical pregnancy and may increase multiple pregnancy when compared to control. Zeng 2018 examined laser AH only in cryopreserved embryos. Their analysis led to the conclusions that AH improved clinical pregnancy rates and increased multiple pregnancy rates when compared to control but led to no difference in live birth rate and miscarriage rate. Our subgroup analysis of cryopreserved embryos includes all methods of AH. Our results suggest that AH makes little to no difference in live birth, clinical pregnancy, or multiple pregnancy when compared to control in this subgroup. Zeng 2018 included studies that reported data outcomes per embryo transfer rather than per woman; this could explain in part the differences in results.

Study flow diagram.

Figures and Tables -
Figure 1

Study flow diagram.

Methodological quality graph: review authors' judgements about each methodological quality item presented as percentages across all included studies.

Figures and Tables -
Figure 2

Methodological quality graph: review authors' judgements about each methodological quality item presented as percentages across all included studies.

Methodological quality summary: review authors' judgements about each methodological quality item for each included study.

Figures and Tables -
Figure 3

Methodological quality summary: review authors' judgements about each methodological quality item for each included study.

Forest plot of comparison: 1 Live birth rate, outcome: 1.1 Live birth per woman randomised.

Figures and Tables -
Figure 4

Forest plot of comparison: 1 Live birth rate, outcome: 1.1 Live birth per woman randomised.

Funnel plot of comparison: 1 Live birth: assisted hatching compared with no assisted hatching, outcome: 1.1 Live birth per woman randomised.

Figures and Tables -
Figure 5

Funnel plot of comparison: 1 Live birth: assisted hatching compared with no assisted hatching, outcome: 1.1 Live birth per woman randomised.

Forest plot of comparison: 4 Multiple pregnancy rate, outcome: 4.1 Multiple pregnancy rate per woman randomised.

Figures and Tables -
Figure 6

Forest plot of comparison: 4 Multiple pregnancy rate, outcome: 4.1 Multiple pregnancy rate per woman randomised.

Forest plot of comparison: 2 Clinical pregnancy, outcome: 2.1 Clinical pregnancy rate per woman randomised.

Figures and Tables -
Figure 7

Forest plot of comparison: 2 Clinical pregnancy, outcome: 2.1 Clinical pregnancy rate per woman randomised.

Funnel plot of comparison: 3 Clinical pregnancy: assisted hatching compared with no assisted hatching, outcome: 3.1 Clinical pregnancy rate per woman randomised.

Figures and Tables -
Figure 8

Funnel plot of comparison: 3 Clinical pregnancy: assisted hatching compared with no assisted hatching, outcome: 3.1 Clinical pregnancy rate per woman randomised.

Funnel plot of comparison: 4 Clinical pregnancies in trials that reported live births: assisted hatching compared with no assisted hatching, outcome: 4.1 Clinical pregnancies in trials reporting live births.

Figures and Tables -
Figure 9

Funnel plot of comparison: 4 Clinical pregnancies in trials that reported live births: assisted hatching compared with no assisted hatching, outcome: 4.1 Clinical pregnancies in trials reporting live births.

Forest plot of comparison: 3 Miscarriage rate, outcome: 3.1 Miscarriage per woman randomised.

Figures and Tables -
Figure 10

Forest plot of comparison: 3 Miscarriage rate, outcome: 3.1 Miscarriage per woman randomised.

Forest plot of comparison: 5 Monozygotic twinning rate, outcome: 5.1 Monozygotic twinning per woman randomised.

Figures and Tables -
Figure 11

Forest plot of comparison: 5 Monozygotic twinning rate, outcome: 5.1 Monozygotic twinning per woman randomised.

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 1: Live birth per woman randomised

Figures and Tables -
Analysis 1.1

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 1: Live birth per woman randomised

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 2: First or repeat attempt

Figures and Tables -
Analysis 1.2

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 2: First or repeat attempt

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 3: Conception mode

Figures and Tables -
Analysis 1.3

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 3: Conception mode

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 4: Hatching method

Figures and Tables -
Analysis 1.4

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 4: Hatching method

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 5: Prognosis

Figures and Tables -
Analysis 1.5

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 5: Prognosis

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 6: Live birth rate by extent of assisted hatching

Figures and Tables -
Analysis 1.6

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 6: Live birth rate by extent of assisted hatching

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 7: Fresh or frozen embryo transfer

Figures and Tables -
Analysis 1.7

Comparison 1: Live birth: assisted hatching compared with no assisted hatching, Outcome 7: Fresh or frozen embryo transfer

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 1: Multiple pregnancy rate per woman randomised

Figures and Tables -
Analysis 2.1

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 1: Multiple pregnancy rate per woman randomised

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 2: First or repeat attempt

Figures and Tables -
Analysis 2.2

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 2: First or repeat attempt

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 3: Conception mode

Figures and Tables -
Analysis 2.3

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 3: Conception mode

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 4: Hatching method

Figures and Tables -
Analysis 2.4

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 4: Hatching method

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 5: Prognosis

Figures and Tables -
Analysis 2.5

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 5: Prognosis

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 6: Multiple pregnancy rate per woman grouped by extent of assisted hatching

Figures and Tables -
Analysis 2.6

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 6: Multiple pregnancy rate per woman grouped by extent of assisted hatching

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 7: Fresh or frozen embryo transfer

Figures and Tables -
Analysis 2.7

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 7: Fresh or frozen embryo transfer

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 8: Multiple pregnancy per pregnancy

Figures and Tables -
Analysis 2.8

Comparison 2: Multiple pregnancy: assisted hatching compared with no assisted hatching, Outcome 8: Multiple pregnancy per pregnancy

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 1: Clinical pregnancy rate per woman randomised

Figures and Tables -
Analysis 3.1

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 1: Clinical pregnancy rate per woman randomised

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 2: First or repeat attempt

Figures and Tables -
Analysis 3.2

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 2: First or repeat attempt

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 3: Conception mode

Figures and Tables -
Analysis 3.3

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 3: Conception mode

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 4: Hatching method

Figures and Tables -
Analysis 3.4

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 4: Hatching method

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 5: Prognosis

Figures and Tables -
Analysis 3.5

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 5: Prognosis

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 6: Extent of assisted hatching

Figures and Tables -
Analysis 3.6

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 6: Extent of assisted hatching

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 7: Fresh and frozen embryo transfer

Figures and Tables -
Analysis 3.7

Comparison 3: Clinical pregnancy: assisted hatching compared with no assisted hatching, Outcome 7: Fresh and frozen embryo transfer

Comparison 4: Clinical pregnancies in trials that reported live births: assisted hatching compared with no assisted hatching, Outcome 1: Clinical pregnancies in trials reporting live births

Figures and Tables -
Analysis 4.1

Comparison 4: Clinical pregnancies in trials that reported live births: assisted hatching compared with no assisted hatching, Outcome 1: Clinical pregnancies in trials reporting live births

Comparison 5: Miscarriage: assisted hatching compared with no assisted hatching, Outcome 1: Miscarriage per woman randomised

Figures and Tables -
Analysis 5.1

Comparison 5: Miscarriage: assisted hatching compared with no assisted hatching, Outcome 1: Miscarriage per woman randomised

Comparison 5: Miscarriage: assisted hatching compared with no assisted hatching, Outcome 2: First or repeat attempt

Figures and Tables -
Analysis 5.2

Comparison 5: Miscarriage: assisted hatching compared with no assisted hatching, Outcome 2: First or repeat attempt

Comparison 5: Miscarriage: assisted hatching compared with no assisted hatching, Outcome 3: Conception mode

Figures and Tables -
Analysis 5.3

Comparison 5: Miscarriage: assisted hatching compared with no assisted hatching, Outcome 3: Conception mode

Comparison 5: Miscarriage: assisted hatching compared with no assisted hatching, Outcome 4: Hatching method

Figures and Tables -
Analysis 5.4

Comparison 5: Miscarriage: assisted hatching compared with no assisted hatching, Outcome 4: Hatching method

Comparison 5: Miscarriage: assisted hatching compared with no assisted hatching, Outcome 5: Prognosis

Figures and Tables -
Analysis 5.5

Comparison 5: Miscarriage: assisted hatching compared with no assisted hatching, Outcome 5: Prognosis

Comparison 5: Miscarriage: assisted hatching compared with no assisted hatching, Outcome 6: Miscarriage per clinical pregnancy

Figures and Tables -
Analysis 5.6

Comparison 5: Miscarriage: assisted hatching compared with no assisted hatching, Outcome 6: Miscarriage per clinical pregnancy

Comparison 6: Monozygotic twinning: assisted hatching compared with no assisted hatching, Outcome 1: Monozygotic twinning per woman randomised

Figures and Tables -
Analysis 6.1

Comparison 6: Monozygotic twinning: assisted hatching compared with no assisted hatching, Outcome 1: Monozygotic twinning per woman randomised

Comparison 7: Robust studies (randomisation method and allocation concealment stated and live birth reported): assisted hatching compared with no assisted hatching, Outcome 1: Live births

Figures and Tables -
Analysis 7.1

Comparison 7: Robust studies (randomisation method and allocation concealment stated and live birth reported): assisted hatching compared with no assisted hatching, Outcome 1: Live births

Comparison 7: Robust studies (randomisation method and allocation concealment stated and live birth reported): assisted hatching compared with no assisted hatching, Outcome 2: Clinical pregnancies

Figures and Tables -
Analysis 7.2

Comparison 7: Robust studies (randomisation method and allocation concealment stated and live birth reported): assisted hatching compared with no assisted hatching, Outcome 2: Clinical pregnancies

Summary of findings 1. Assisted hatching compared to no assisted hatching for women undergoing assisted conception

Assisted hatching compared to no assisted hatching for women undergoing assisted conception

Patient or population: women undergoing assisted conception

Setting: clinic
Intervention: assisted hatching
Comparison: no assisted hatching

Outcomes

Anticipated absolute effects* (95% CI)

Relative effect
(95% CI)

№. of participants
(studies)

Quality of evidence
(GRADE)

Comments

Risk with no assisted hatching

Risk with assisted hatching

Live births per woman randomised

283 per 1000

301 per 1000
(267 to 338)

OR 1.09
(0.92 to 1.29)

2849
(14 RCTs)

⊕⊕⊝⊝
LOWa

Multiple pregnancy rate per woman randomised

91 per 1000

121 per 1000
(102 to 144)

OR 1.38
(1.13 to 1.68)

4308
(18 RCTs)

⊕⊕⊝⊝
LOWb

Clinical pregnancy rate per woman randomised

322 per 1000

363 per 1000
(341 to 387)

OR 1.20
(1.09 to 1.33)

7249
(39 RCTs)

⊕⊕⊝⊝
LOWb

Miscarriage rate per woman randomised

53 per 1000

60 per 1000
(44 to 81)

OR 1.13
(0.82 to 1.56)

2810
(17 RCTs)

⊕⊝⊝⊝
VERY LOWc

*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: confidence interval; OR: odds ratio; RCT: randomised controlled trial.

GRADE Working Group grades of evidence.
High quality: we are very confident that the true effect lies close to that of the estimate of the effect.
Moderate quality: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.
Low quality: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect.
Very low quality: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.

aDowngraded two levels for serious risk of bias and publication bias: in many studies, the method was unclear and information was incomplete. The main limitation was serious risk of bias associated with poor reporting of study methods.

bDowngraded two levels for serious risk of bias and for serious inconsistency.

cDowngraded three levels for serious risk of bias, serious inconsistency, and serious imprecision (only 158 events).

Figures and Tables -
Summary of findings 1. Assisted hatching compared to no assisted hatching for women undergoing assisted conception
Table 1. Mean age of participants in assisted hatching and control groups

Study

AH n, mean age (SD)

Control n, mean age (SD)

OR for clinical pregnancy

Abulsoud 2019

65, 39.2 (1.2)

65, 39.5 (1.2)

2.50 (1.14 to 5.49)

Antinori 1999: first IVF

73, 37.5

69, 36.0

1.27 (0.70 to 2.32)

Antinori 1999: repeat IVF

96, 27.5

103, 27

1.86 (0.81 to 4.25)

Balaban 2006

183, 32.4 (3.3)

183, 32.7 (3.1)

1.85 (1.19 to 2.86)

Balakier 2009

45, 32.5 (3.8)

39, 33.8 (3.2)

0.64 (0.27 to 1.55)

Baruffi 2000

51, 31.8 (3.6)

52, 31.4 (3.6)

0.74 (0.33 to 1.65)

Carter 2003

121, 34 (3.3)

82, 34 (3.2)

0.95 (0.54 to 1.67)

Ciray 2005

60, 33.1 (4.2)

30, 34.0 (3.7)

0.62 (0.26 to 1.49)

Cohen 1992: FSH < 15

69, 36.50 (3.30)

68, 36.70 (3.70)

2.11 (1.18 to 3.77)

Cohen 1992: poor prognosis

80, 36.7 (4.3)

83, 35.3 (4.2)

1.30 (0.66 to 2.55)

Cohen 1992: FSH > 15

not stated

not stated

1.30 (0.66 to 2.55)

Elhelw 2005

not stated

not stated

1.77 (0.52 to 6.01)

Elnahas 2017

80, 31.0 (4.7)

80, 31.7 (4.9)

1.58 (0.81 to 3.08)

Fang 2010

61, 32.3 (3.4)

64, 32.1 (3.6)

2.37 (1.07 to 5.28)

Ge 2008: fresh embryo

387, 31.08 (4.68)

373, 30.44 (4.15)

0.99 (0.74 to 1.32)

Ge 2008: frozen embryo

100, 31.84 (3.85)

100, 30.66 (4.42)

2.05 (0.99 to 4.22)

Germond 2004: first cycle of frozen‐thawed embryos

62, 32.8 (4.2)

53, 32.6 (3.8)

0.09 (0.01 to 0.76)

Germond 2004: poor prognosis, first cycle of fresh embryos

22, 39.3 (2.9)

21, 38.3 (3.4)

0.51 (0.10 to 2.45)

González‐Ortega 2015

154, 38.5 (2.8)

149, 37.3 (4.2)

2.71 (1.62 to 4.56)

Hagemann 2010

59, 32.1 (3.0)

62, 31.2 (3.5)

0.81 (0.37 to 1.76)

Hellebaut 1996

60, 30.9 (4.3)

60, 30.8 (3.9)

1.15 (0.55 to 2.43)

Hurst 1998

13, 30.0 (0.9)

7, 30.0 (0.8)

0.40 (0.06 to 2.89)

Isik 2000

24, 30.5 (5.2)

22, 29.1 (3.6)

2.0 (0.62 to 6.49)

Isiklar 1999

not stated

not stated

3.20 (0.91 to 11.27)

Jelinkova 2002

128, 32.3 (4.24)

129, 32.1 (3.16)

1.86 (1.12 to 3.10)

Kutlu 2010: good prognosis

73, 29.9 (2.9)

66, 28.9 (3.4)

1.06 (0.54 to 2.08)

Kutlu 2010: poor prognosis

58, 38.0 (2.3)

55, 37.4 (2.4)

1.23 (0.58 to 2.60)

Laffoon 1999

not stated

not stated

0.85 (0.28 to 2.58)

Lanzendorf 1998

41, 38.30 (0.31)

48, 38.50 (0.26)

0.90 (0.38 to 2.10)

Nada 2018

158, 31.3 (4.1)

150, 32.6 (2.4)

1.79 (1.05 to 3.07)

Nagy 1999

20, 32.0 (4.0)

20, 31.4 (3.7)

8.0 (1.44 to 44.3)

Ng 2005

80, 34.0 (range 25 to 40)

80, 34.0 (range 26 to 40)

0.81 (0.33 to 2.00)

Petersen 2005: 1 previous implantation failure

35, 34.6 (4.6)

35, 34.1 (5.3)

1.15 (0.41 to 3.19)

Petersen 2005: several previous implantation failures

40, 35.7 (3.8)

40, 35.3 (5.1)

4.11 (1.04 to 16.29)

Razi 2013

90, 32.9 (0.5)

92, 31.6 (0.4)

0.7 (0.3 to 1.6)

Rufas‐Sapir 2004

not stated

not stated

0.72 (0.38 to 1.36)

Ryan 1997

not stated

not stated

0.74 (0.35 to 1.59)

Safari 2017

30, 30.6 (5.6)

32, 29.2 (5.3)

0.58 (0.19 to 1.78)

Sagoskin 2007

118, 34.0 (3.3)

81, 34.0 (3.2)

0.94 (0.53 to1.65)

Shi 2016

82, 37.2 (2.22)

96, 36.97 (1.96)

0.65 (0.36 to 1.18)

Stein 1995

not stated

not stated

1.54 (0.67 to 3.54)

Tucker 1993

110, 34.1 (4.8)

108, 34.2 (4.1)

1.37 (0.79 to 2.35)

Tucker 1996

50, 35.3 (4.2)

50, 33.5 (4.3)

0.74 (0.35 to 1.59)

Utsunomiya 1998

not stated

not stated

1.36 (0.32 to 5.73)

Valojerdi 2010

200, 30.86 (5.82)

200, 29.85 (5.14)

0.53 (0.35 to 0.80)

Wan 2014

96, 33.1 (3.7)

102, 32.6 (3.4)

1.91 (1.08 to 3.38)

Figures and Tables -
Table 1. Mean age of participants in assisted hatching and control groups
Table 2. Prognostic factors in included trials

Study ID

Balanced age between groups

Balances no. of embryos transferred

Prognosis: poor/good

FSH levels

Blastocyst transfer

Complete/partial AH

Frozen cycles

Abulsoud 2019

Yes

Yes

Poor

No data

No

Thinning

Fresh

Antinori 1999

AH mean 1.5 years older

Yes

Good and poor subgroups

No data

No

Complete hole

Not stated

Balaban 2006

Yes

Yes

Unselected

< 10

No

Thinning

Frozen

Balakier 2009

AH mean 1.3 years older

Yes

Good

< 10

No

Thinning

Fresh

Baruffi 2000

Yes

Yes

Good

No data

No

Thinning

Fresh

Carter 2003

Yes

Yes

Good

< 10

No

Not stated

Fresh

Ciray 2005

Yes

Yes

Good

< 15

No

Thinning

Fresh

Cohen 1992

Yes

Yes

Unstated

≤ 15 and > 15 subgroups

No

Complete hole

Fresh

Elhelw 2005

Yes

No data

Poor

No data

No

Thinning

Frozen

Elnahas 2017

Yes

No data

Good

No data

No

Thinning

Frozen

Fang 2010

Yes

Yes

Not stated

No data

No

Mechanical expansion

Frozen thawed

Ge 2008

Yes

Yes

Mixed

No data

No

Thinning

Fresh and frozen subgroups

Germond 2004

Yes

Yes

Mixed, in subgroups

Between 3 and 12

No

Complete hole

Fresh and frozen subgroups

González‐Ortega 2015

Yes

Yes

Poor

> 12

No

Partial

Fresh

Hagemann 2010

Mean age data given only for combined cycles 1 and 2

Yes

Under 38 years, > 2 previously failed cycles, ZP thickness > 13 micrometers

No data

No

20 micrometer diameter opening

Fresh

Hellebaut 1996

Yes

Yes

Good

No data

No

Complete hole

Fresh

Hurst 1998

Yes

Yes

Good

< 10

No

Complete hole

Fresh

Isik 2000

AH mean 1.4 years older

Yes

Unstated

< 10

Yes

Removal complete

Fresh

Isiklar 1999

No data

Yes

Unstated

No data

Yes

Complete hole

Fresh

Jelinkova 2002

Yes

Yes

Poor

No data

Yes

Removal complete

Fresh

Kutlu 2010

Yes

Yes

Good and poor subgroups

No data

No

Complete hole

Fresh

Laffoon 1999

No data

No data

Good

No data

No

Complete hole

Fresh

Lanzendorf 1998

No

Yes

Poor

No data

No

Complete hole

Fresh

Nada 2018

Yes

Yes

Good

AH 5.4 ± 1.3
No AH 6.0 ± 1.1

No

Thinning

Fresh

Nagy 1999

Yes

Yes

Unstated

No data

No

Thinning

Frozen‐thaw cycle

Ng 2005

Yes

Higher proportion of controls received 3 embryos

Unstated

< 11

No

Thinning

Frozen‐thaw cycle

Petersen 2005

Yes

Yes

Poor

No data

No

Thinning

Fresh

Razi 2013

Yes

Yes

Unstated

No data

No

Partial

Fresh

Rufas‐Sapir 2004

No data

Yes

Poor

No data

No

Complete hole

Fresh

Ryan 1997

No data

No data

Unstated

No data

No

Complete hole

Both

Safari 2017

Yes

Yes

Unstated

AH 6.4 ± 2.3

No AH 5.6 ± 2.1

No

Thinning

Frozen

Sagoskin 2007

Yes

Yes

Good

< 10

No

Hole

Fresh

Shi 2016

Yes

Yes

Advanced maternal age

< 10

No

Zona Thinning

Fresh

Stein 1995

No data

No data

Poor

No data

No

Complete hole

Fresh

Tucker 1993

Yes

Yes

Good

< 15

No

Thinning

Fresh

Tucker 1996

AH mean 1.8 years older

Yes

Not stated

No data

No

Complete hole

Fresh

Utsunomiya 1998

No data

No data

Poor

No data

No

Thinning

Fresh

Valojerdi 2010

Yes

Yes

Not stated

No data

No

Partially thinned

Vitrified‐warmed embryo

Wan 2014

Yes

Yes

Previously unsuccessful 1 fresh cycle

No data

Yes

Partial

Vitrified‐warmed embryo

AH: assisted hatching.
ET: embryo transfer.
FSH: follicle‐stimulating hormone.

Figures and Tables -
Table 2. Prognostic factors in included trials
Comparison 1. Live birth: assisted hatching compared with no assisted hatching

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

1.1 Live birth per woman randomised Show forest plot

14

2849

Odds Ratio (M‐H, Fixed, 95% CI)

1.09 [0.92, 1.29]

1.2 First or repeat attempt Show forest plot

4

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

1.2.1 First attempt at IVF or ICSI

3

380

Odds Ratio (M‐H, Fixed, 95% CI)

0.78 [0.48, 1.28]

1.2.2 Repeat attempt at IVF or ICSI

1

150

Odds Ratio (M‐H, Fixed, 95% CI)

1.40 [0.62, 3.13]

1.3 Conception mode Show forest plot

6

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

1.3.1 ICSI only

3

640

Odds Ratio (M‐H, Fixed, 95% CI)

1.54 [1.02, 2.33]

1.3.2 IVF only

3

241

Odds Ratio (M‐H, Fixed, 95% CI)

1.00 [0.60, 1.68]

1.4 Hatching method Show forest plot

14

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

1.4.1 Chemical

4

366

Odds Ratio (M‐H, Fixed, 95% CI)

1.13 [0.74, 1.74]

1.4.2 Laser

10

2473

Odds Ratio (M‐H, Fixed, 95% CI)

1.07 [0.89, 1.28]

1.5 Prognosis Show forest plot

9

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

1.5.1 Poor prognosis

4

576

Odds Ratio (M‐H, Fixed, 95% CI)

1.46 [0.99, 2.15]

1.5.2 Good prognosis

6

1495

Odds Ratio (M‐H, Fixed, 95% CI)

1.03 [0.83, 1.28]

1.6 Live birth rate by extent of assisted hatching Show forest plot

14

2849

Odds Ratio (M‐H, Fixed, 95% CI)

1.09 [0.92, 1.29]

1.6.1 Thinning only

6

1742

Odds Ratio (M‐H, Fixed, 95% CI)

1.06 [0.86, 1.30]

1.6.2 Breach by hole only

8

1107

Odds Ratio (M‐H, Fixed, 95% CI)

1.15 [0.87, 1.51]

1.7 Fresh or frozen embryo transfer Show forest plot

12

1731

Odds Ratio (M‐H, Fixed, 95% CI)

1.14 [0.92, 1.41]

1.7.1 Fresh

11

1669

Odds Ratio (M‐H, Fixed, 95% CI)

1.16 [0.94, 1.44]

1.7.2 Frozen

1

62

Odds Ratio (M‐H, Fixed, 95% CI)

0.67 [0.22, 2.07]

Figures and Tables -
Comparison 1. Live birth: assisted hatching compared with no assisted hatching
Comparison 2. Multiple pregnancy: assisted hatching compared with no assisted hatching

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

2.1 Multiple pregnancy rate per woman randomised Show forest plot

18

4308

Odds Ratio (M‐H, Fixed, 95% CI)

1.38 [1.13, 1.68]

2.2 First or repeat attempt Show forest plot

8

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

2.2.1 First attempt at IVF or ICSI

4

654

Odds Ratio (M‐H, Fixed, 95% CI)

0.73 [0.31, 1.72]

2.2.2 Repeat attempt at IVF or ICSI

5

1068

Odds Ratio (M‐H, Fixed, 95% CI)

1.25 [0.80, 1.94]

2.3 Conception mode Show forest plot

9

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

2.3.1 ICSI only

3

573

Odds Ratio (M‐H, Fixed, 95% CI)

3.09 [1.57, 6.08]

2.3.2 IVF only

6

1126

Odds Ratio (M‐H, Fixed, 95% CI)

1.87 [1.28, 2.72]

2.4 Hatching method Show forest plot

18

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

2.4.1 Chemical

4

534

Odds Ratio (M‐H, Fixed, 95% CI)

1.55 [0.98, 2.47]

2.4.2 Laser

13

3730

Odds Ratio (M‐H, Fixed, 95% CI)

1.29 [1.03, 1.61]

2.4.3 Mechanical

1

44

Odds Ratio (M‐H, Fixed, 95% CI)

8.33 [1.56, 44.64]

2.5 Prognosis Show forest plot

10

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

2.5.1 Poor prognosis

6

1186

Odds Ratio (M‐H, Fixed, 95% CI)

1.95 [1.27, 3.00]

2.5.2 Good prognosis

6

1569

Odds Ratio (M‐H, Fixed, 95% CI)

1.08 [0.81, 1.44]

2.6 Multiple pregnancy rate per woman grouped by extent of assisted hatching Show forest plot

16

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

2.6.1 Thinning only

6

2148

Odds Ratio (M‐H, Fixed, 95% CI)

1.34 [1.02, 1.76]

2.6.2 Breach by hole

9

1629

Odds Ratio (M‐H, Fixed, 95% CI)

1.51 [1.08, 2.11]

2.6.3 Complete removal of zona

1

25

Odds Ratio (M‐H, Fixed, 95% CI)

0.62 [0.07, 5.28]

2.7 Fresh or frozen embryo transfer Show forest plot

16

3190

Odds Ratio (M‐H, Fixed, 95% CI)

1.38 [1.08, 1.75]

2.7.1 Fresh

13

2264

Odds Ratio (M‐H, Fixed, 95% CI)

1.30 [0.98, 1.73]

2.7.2 Frozen

3

926

Odds Ratio (M‐H, Fixed, 95% CI)

1.60 [1.00, 2.55]

2.8 Multiple pregnancy per pregnancy Show forest plot

17

1598

Odds Ratio (M‐H, Fixed, 95% CI)

1.37 [1.09, 1.72]

Figures and Tables -
Comparison 2. Multiple pregnancy: assisted hatching compared with no assisted hatching
Comparison 3. Clinical pregnancy: assisted hatching compared with no assisted hatching

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

3.1 Clinical pregnancy rate per woman randomised Show forest plot

39

7249

Odds Ratio (M‐H, Fixed, 95% CI)

1.20 [1.09, 1.33]

3.2 First or repeat attempt Show forest plot

18

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

3.2.1 First attempt at IVF or ICSI

8

1010

Odds Ratio (M‐H, Fixed, 95% CI)

0.74 [0.56, 0.98]

3.2.2 Repeat attempt at IVF or ICSI

11

1798

Odds Ratio (M‐H, Fixed, 95% CI)

1.65 [1.34, 2.04]

3.3 Conception mode Show forest plot

26

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

3.3.1 ICSI only

11

1825

Odds Ratio (M‐H, Fixed, 95% CI)

1.40 [1.14, 1.71]

3.3.2 IVF only

15

2460

Odds Ratio (M‐H, Fixed, 95% CI)

1.31 [1.10, 1.55]

3.4 Hatching method Show forest plot

39

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

3.4.1 Chemical

11

1536

Odds Ratio (M‐H, Fixed, 95% CI)

1.33 [1.08, 1.64]

3.4.2 Laser

23

5127

Odds Ratio (M‐H, Fixed, 95% CI)

1.15 [1.03, 1.30]

3.4.3 Mechanical

5

586

Odds Ratio (M‐H, Fixed, 95% CI)

1.30 [0.89, 1.88]

3.5 Prognosis Show forest plot

24

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

3.5.1 Poor prognosis

14

2108

Odds Ratio (M‐H, Fixed, 95% CI)

1.68 [1.38, 2.04]

3.5.2 Good prognosis

14

2721

Odds Ratio (M‐H, Fixed, 95% CI)

1.10 [0.94, 1.29]

3.6 Extent of assisted hatching Show forest plot

37

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

3.6.1 Thinning only

17

3774

Odds Ratio (M‐H, Fixed, 95% CI)

1.10 [0.96, 1.26]

3.6.2 Breach by hole only

17

2543

Odds Ratio (M‐H, Fixed, 95% CI)

1.17 [0.98, 1.39]

3.6.3 Complete removal of zona

2

301

Odds Ratio (M‐H, Fixed, 95% CI)

1.93 [1.21, 3.09]

3.6.4 Expansion of zona pellucida

1

125

Odds Ratio (M‐H, Fixed, 95% CI)

2.37 [1.07, 5.28]

3.7 Fresh and frozen embryo transfer Show forest plot

38

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

3.7.1 Fresh embryo transfer

30

5349

Odds Ratio (M‐H, Fixed, 95% CI)

1.23 [1.10, 1.38]

3.7.2 Frozen embryo transfer only

10

1700

Odds Ratio (M‐H, Fixed, 95% CI)

1.15 [0.93, 1.42]

Figures and Tables -
Comparison 3. Clinical pregnancy: assisted hatching compared with no assisted hatching
Comparison 4. Clinical pregnancies in trials that reported live births: assisted hatching compared with no assisted hatching

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

4.1 Clinical pregnancies in trials reporting live births Show forest plot

14

2849

Odds Ratio (M‐H, Fixed, 95% CI)

1.07 [0.92, 1.25]

Figures and Tables -
Comparison 4. Clinical pregnancies in trials that reported live births: assisted hatching compared with no assisted hatching
Comparison 5. Miscarriage: assisted hatching compared with no assisted hatching

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

5.1 Miscarriage per woman randomised Show forest plot

17

2810

Odds Ratio (M‐H, Fixed, 95% CI)

1.13 [0.82, 1.56]

5.2 First or repeat attempt Show forest plot

8

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

5.2.1 First attempt at IVF or ICSI

4

442

Odds Ratio (M‐H, Fixed, 95% CI)

0.98 [0.51, 1.89]

5.2.2 Repeat attempt at IVF or ICSI

5

966

Odds Ratio (M‐H, Fixed, 95% CI)

1.96 [0.90, 4.28]

5.3 Conception mode Show forest plot

10

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

5.3.1 ICSI only

4

665

Odds Ratio (M‐H, Fixed, 95% CI)

1.20 [0.58, 2.47]

5.3.2 IVF only

6

896

Odds Ratio (M‐H, Fixed, 95% CI)

1.28 [0.65, 2.52]

5.4 Hatching method Show forest plot

17

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

5.4.1 Chemical

5

412

Odds Ratio (M‐H, Fixed, 95% CI)

1.11 [0.56, 2.21]

5.4.2 Laser

11

2244

Odds Ratio (M‐H, Fixed, 95% CI)

1.13 [0.78, 1.64]

5.4.3 Mechanical

1

154

Odds Ratio (M‐H, Fixed, 95% CI)

1.14 [0.07, 18.58]

5.5 Prognosis Show forest plot

11

Odds Ratio (M‐H, Fixed, 95% CI)

Subtotals only

5.5.1 Poor prognosis

7

1133

Odds Ratio (M‐H, Fixed, 95% CI)

1.21 [0.70, 2.08]

5.5.2 Good prognosis

5

626

Odds Ratio (M‐H, Fixed, 95% CI)

1.03 [0.50, 2.14]

5.6 Miscarriage per clinical pregnancy Show forest plot

15

777

Odds Ratio (M‐H, Random, 95% CI)

0.94 [0.62, 1.43]

Figures and Tables -
Comparison 5. Miscarriage: assisted hatching compared with no assisted hatching
Comparison 6. Monozygotic twinning: assisted hatching compared with no assisted hatching

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

6.1 Monozygotic twinning per woman randomised Show forest plot

6

729

Odds Ratio (M‐H, Fixed, 95% CI)

3.23 [0.34, 31.03]

Figures and Tables -
Comparison 6. Monozygotic twinning: assisted hatching compared with no assisted hatching
Comparison 7. Robust studies (randomisation method and allocation concealment stated and live birth reported): assisted hatching compared with no assisted hatching

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

7.1 Live births Show forest plot

1

960

Odds Ratio (M‐H, Fixed, 95% CI)

1.08 [0.82, 1.41]

7.2 Clinical pregnancies Show forest plot

1

960

Odds Ratio (M‐H, Fixed, 95% CI)

1.10 [0.85, 1.43]

Figures and Tables -
Comparison 7. Robust studies (randomisation method and allocation concealment stated and live birth reported): assisted hatching compared with no assisted hatching