Types of studies

Randomised controlled trials (RCTs) only. (We will not include results from quasi RCTs in the analyses but we may discuss them in the text if little other evidence is available.)

Types of participants

Women in labour. (This will include women in high‐risk groups, e.g. preterm labour or following induction of labour. We will use subgroup analysis to look for any possible differences in the effect of interventions in these groups.)

Types of interventions

These reviews contribute to an overview of systematic reviews of interventions for pain management in labour (in preparation), and share a generic protocol (in preparation). To avoid duplication, the different methods of pain management have been listed in a specific order, from one to 15. Individual reviews focusing on particular interventions include comparisons with only the intervention above it on the list. We will add methods of pain management identified in the future to the end of the list. The current list is as follows.

1. Placebo/no treatment

2. Hypnosis (Madden 2011)

3. Biofeedback (Barragán 2011)

4. Intracutaneous or subcutaneous sterile water injection (Derry 2011)

5. Immersion in water (Cluett 2009)

6. Aromatherapy (Smith 2011b)

7. Relaxation techniques (yoga, music, audio) (this review)

8. Acupuncture or acupressure (Smith 2011a)

9. Manual methods (massage, reflexology) (Smith 2011c)

10. Transcutaneous electrical nerve stimulation (TENS) (Dowswell 2009)

11. Inhaled analgesia (Klomp 2011)

12. Opioid drugs (Ullman 2010)

13. Non‐opioid drugs (Othman 2011)

14. Local anaesthetic nerve blocks (Novikova 2011)

15. Epidural (including combined spinal‐epidural) (Anim‐Somuah 2005; Simmons 2007)

Accordingly, this review will include comparisons of one form of relaxation technique compared with any other type of relaxation technique, or relaxation compared with 1. placebo/no treatment/usual care; 2. hypnosis; 3. biofeedback; 4. intracutaneous or subcutaneous sterile water injection; 5. immersion in water; or 6. aromatherapy.

Types of outcome measures

This review is one in a series of Cochrane reviews examining pain management in labour. These reviews contribute to an overview of systematic reviews of interventions for pain management in labour, and share a generic protocol. The following list of primary outcomes are the ones which are common to all the reviews.

Electronic searches

We searched the Cochrane Pregnancy and Childbirth Group’s Trials Register by contacting the Trials Search Co‐ordinator (30 November 2010). 

The Cochrane Pregnancy and Childbirth Group’s Trials Register is maintained by the Trials Search Co‐ordinator and contains trials identified from: 

1. quarterly searches of the Cochrane Central Register of Controlled Trials (CENTRAL);

2. weekly searches of MEDLINE;

3. weekly searches of EMBASE;

4. handsearches of 30 journals and the proceedings of major conferences;

5. weekly current awareness alerts for a further 44 journals plus monthly BioMed Central email alerts.

Details of the search strategies for CENTRAL, MEDLINE and EMBASE, the list of handsearched journals and conference proceedings, and the list of journals reviewed via the current awareness service can be found in the ‘Specialized Register’ section within the editorial information about the Cochrane Pregnancy and Childbirth Group. 

Trials identified through the searching activities described above are each assigned to a review topic (or topics). The Trials Search Co‐ordinator searched the register for each review using the topic list rather than keywords.

We searched the Cochrane Complementary Medicine Field's Trials Register using the terms (labor OR labour).

In addition, we searched the Cochrane Central Register of Controlled Trials (The Cochrane Library 2010, Issue 4) (Appendix 1), MEDLINE (1966 to 30 November 2010) (Appendix 2), and CINAHL (1980 to 30 November 2010) (Appendix 3).

We also searched the following for ongoing or unpublished trials: the Australian and New Zealand Trials Registry (30 November 2010); the Chinese Clinical Trial Register (30 November 2010); Current Controlled Trials (30 November 2010); ClinicalTrials.gov (30 November 2010); the ISRCTN Register; (30 November 2010); National Centre for Complementary and Alternative Medicine (NCCAM) (30 November 2010); and the WHO International Clinical Trials Registry Platform (ICTRP). (30 November 2010). See:Appendix 4 for search terms used in these sources.

We did not apply any language restrictions.

Selection of studies

Three review authors (C Smith (CS), CT Collins (CTC) and K Levett (KL)) screened the titles and abstracts of articles found in the search, and discarded trials that were clearly not eligible. Two out of the three review authors (CS, CTC, KL) undertook trial selection.

CS, KL and CTC independently assessed whether the trials met the inclusion criteria, with disagreements resolved by discussion with the fourth author (C Crowther). When articles contained insufficient information to make a decision about eligibility, CS attempted to contact authors of the original reports to obtain further details.

Data extraction and management

Following an assessment for inclusion, CS, KL or CTC independently extracted data using the form designed by the Review Group for this purpose. We resolved discrepancies through discussion or, if required, we consulted a fourth person. For each included trial, we collected information regarding the location of the trial, methods of the trial (as per assessment of risk of bias), the participants (age range, eligibility criteria), the nature of the interventions and data relating to the outcomes specified above. We collected information on reported benefits and adverse effects. When information regarding any of the above was unclear, we attempted to contact authors of the original reports to provide further details. We entered data into Review Manager software (RevMan 2011) and checked for accuracy.

Assessment of risk of bias in included studies

Two review authors independently assessed the risk of bias for each study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). We resolved any disagreement by discussion or by involving a third assessor.

The tool consists of six items. There are three potential responses: high risk, low risk or unclear risk. We also made a judgement of ‘unclear’ if what happened in the study was known but the risk of bias was unknown; or if an entry was not relevant to the study at hand (particularly for assessing blinding and incomplete outcome data, or when the outcome being assessed by the entry has not been measured in the study).

We assessed the following characteristics: sequence generation, allocation concealment, blinding (or masking), incomplete data assessment, selective outcome reporting, other sources of bias, described below. We generated a 'risk of bias assessment' table for each study.

Measures of treatment effect

Unit of analysis issues

We included cluster‐randomised trials in the analyses along with individually randomised trials, and adjusted their sample sizes using the methods described in the Handbook using an estimate of the intra‐cluster correlation co‐efficient (ICC) derived from the trial (if possible), from a similar trial or from a study of a similar population. If we used ICCs from other sources, we would report this and conduct sensitivity analyses to investigate the effect of variation in the ICC. If we identified both cluster‐randomised trials and individually‐randomised trials, we planned to synthesise the relevant information. We considered it reasonable to combine the results from both if there was little heterogeneity between the study designs and the interaction between the effect of intervention and the choice of randomisation unit was considered to be unlikely. We would also acknowledge heterogeneity in the randomisation unit and perform a sensitivity analysis to investigate the effects of the randomisation unit.

Dealing with missing data

For included studies, we noted levels of attrition. We aimed to explore the impact of including studies with high levels of missing data in the overall assessment of treatment effect by using sensitivity analysis.

For all outcomes, we carried out analyses, as far as possible, on an intention‐to‐treat basis, i.e. we attempted to include all participants randomised to each group in the analyses, and analysed all participants in the group to which they were allocated, regardless of whether or not they received the allocated intervention. The denominator for each outcome in each trial was the number randomised minus any participants whose outcomes are known to be missing. We excluded trials with greater than 20% missing data from the analysis.

Assessment of heterogeneity

We assessed statistical heterogeneity in each meta‐analysis using the T², I² and Chi² statistics. We regarded heterogeneity as substantial if T² was greater than zero and either I² was greater than 50% or there was a low P value (less than 0.10) in the Chi² test for heterogeneity.

Assessment of reporting biases

If there were 10 or more studies in the meta‐analysis we planned to investigate reporting biases (such as publication bias) using funnel plots. We would assess funnel plot asymmetry visually, and would use formal tests for funnel plot asymmetry. For continuous outcomes we would use the test proposed by Egger 1997, and for dichotomous outcomes we would use the test proposed by Harbord 2006. If asymmetry was detected in any of these tests or was suggested by a visual assessment, we proposed to perform exploratory analyses to investigate it.

Data synthesis

We carried out statistical analysis using the Review Manager software (RevMan 2011). We used fixed‐effect meta‐analysis for combining data where it was reasonable to assume that studies were estimating the same underlying treatment effect: i.e. where trials were examining the same intervention, and the trials’ populations and methods were judged sufficiently similar. If there was clinical heterogeneity sufficient to expect that the underlying treatment effects differed between trials, or if substantial statistical heterogeneity was detected, we used a random‐effects meta‐analysis to produce an overall summary if an average treatment effect across trials was considered clinically meaningful. We treated the random‐effects summary as the average range of possible treatment effects and we discussed the clinical implications of treatment effects differing between trials. If the average treatment effect was not clinically meaningful we have not combined trials.

If we used the random‐effects analyses, we have presented the results as the average treatment effect with its 95% confidence interval, and the estimates of  T² and I².

Subgroup analysis and investigation of heterogeneity

We investigated substantial heterogeneity was investigated using subgroup analyses and sensitivity analyses. We considered whether an overall summary was meaningful, and if it was, a random‐effects analysis was undertaken.

We planned to carry out the following subgroup analyses.

1. Spontaneous labour versus induced labour.

2. Primiparous versus multiparous.

3. Term versus preterm birth.

4. Continuous support in labour versus no continuous support.

We judged subgroup differences by the results of interaction tests produced by RevMan.

Sensitivity analysis

Where subgroup analysis failed to explain the heterogeneity, we planned to analyse the data using the random‐effects model. A priori, we planned to perform sensitivity analyses on results to look at the possible contribution of: (1) differences in methodological quality, with trials of high quality (low risk of bias) compared to all trials; and (2) publication bias by country. If publication bias was present we planned to undertake a sensitivity analysis excluding trials from countries where there was a greater publication bias.