Primary outcomes

1. Postpartum haemorrhage: estimated blood loss greater than 1000 mL immediately or delayed after caesarean section

Secondary outcomes

1. Need for blood transfusion: blood transfusion given during or within 24 hours after caesarean section

2. Hematocrit or haemoglobin concentration: concentration of hematocrit or haemoglobin at postoperative period, or the change in concentration compared to preoperative or baseline level

3. Secondary postpartum haemorrhage: late vaginal bleeding, within six weeks postpartum

4. Febrile morbidity: temperature of 38 degrees Celsius or higher on any two of the first 10 days postpartum, exclusive of the first 24 hours, of unknown causes

5. Endometritis: febrile morbidity due to intrauterine infection, clinically diagnosed by fever, uterine tenderness, foul‐smelling discharge, or a combination

6. Cervical trauma: signs of vaginal bleeding due to the tear of cervical tissue from mechanical dilatation

7. Uterine subinvolution: delayed or absent involution of the uterus during the postpartum period

Based on the included studies in the first version of this review, we added these secondary outcomes.

1. Blood loss: estimated blood loss recorded during and immediately after caesarean section

2. Wound infection: presence of purulent or serous wound discharge with induration, warmth, and tenderness

3. Urinary tract infection: clinical signs plus identification of micro‐organisms of 10⁵ on culture

4. Operative time: duration of operative time

Based on the ongoing studies identified after searching the trial registers for this update of the review, we added these secondary outcomes.

1. Infectious morbidity: rate of endometritis, wound infection, febrile morbidity, and urinary tract infection.

2. Endometrial cavity thickness: the decidual thickness and the intracavitary fluid collection measured by transabdominal ultrasound in mm

3. Retained products of conception: necessity of oxytocin administration, cervical dilatation, or curettage within six weeks

4. Integrity of uterine scar: scar thickness less than 2.3 mm

5. Distortion of uterine incision: any deviation from the full thickness apposition of the anterior uterine wall

6. Healing ratio: anterior wall thickness/anterior wall thickness + height of the wedge‐shaped defect

(1) Random sequence generation (checking for possible selection bias)

For each included study, we described the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups.

We assessed the method as:

• low risk of bias (any truly random process, e.g. random number table; computer random number generator);

• high risk of bias (any non‐random process, e.g. odd or even date of birth; hospital or clinic record number);

• unclear risk of bias.

(2) Allocation concealment (checking for possible selection bias)

For each included study, we described the method used to conceal allocation to interventions prior to assignment, and assessed whether intervention allocation could have been foreseen in advance of, or during recruitment, or changed after assignment.

We assessed the methods as:

• low risk of bias (e.g. telephone or central randomisation; consecutively numbered, sealed, opaque envelopes);

• high risk of bias (open random allocation; unsealed or non‐opaque envelopes, alternation; date of birth);

• unclear risk of bias.

(3.1) Blinding of participants and personnel (checking for possible performance bias)

For each included study, we described the methods used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. We considered that studies were at low risk of bias if they were blinded, or if we judged that the lack of blinding was unlikely to affect results. We assessed blinding separately for different outcomes or classes of outcomes.

We assessed the methods as:

• low, high or unclear risk of bias for participants;

• low, high or unclear risk of bias for personnel.

(3.2) Blinding of outcome assessment (checking for possible detection bias)

For each included study, we described the methods used, if any, to blind outcome assessors from knowledge of which intervention a participant received. We assessed blinding separately for different outcomes or classes of outcomes.

We assessed methods used to blind outcome assessment as:

• low, high, or unclear risk of bias.

(4) Incomplete outcome data (checking for possible attrition bias due to the amount, nature and handling of incomplete outcome data)

For each included study, and for each outcome or class of outcomes, we described the completeness of data, including attrition and exclusions from the analysis. We stated whether attrition and exclusions were reported, and the numbers included in the analysis at each stage (compared with the total randomised participants), reasons for attrition or exclusion where reported, and whether missing data were balanced across groups, or were related to outcomes. Where sufficient information was reported, or could be supplied by the trial authors, we planned to re‐include missing data in the analyses that we undertook.

We assessed methods as:

• low risk of bias (e.g. no missing outcome data; missing outcome data balanced across groups);

• high risk of bias (e.g. numbers or reasons for missing data imbalanced across groups; ‘as treated’ analysis done with substantial departure of intervention received from that assigned at randomisation) or greater than 20% of missing outcome;

• unclear risk of bias.

(5) Selective reporting (checking for reporting bias)

For each included study, we described how we investigated the possibility of selective outcome reporting bias and what we found.

We assessed the methods as:

• low risk of bias (where it was clear that all of the study’s pre‐specified outcomes in the methods section and all expected outcomes of interest to the review were reported);

• high risk of bias (where not all the study’s pre‐specified outcomes were reported; one or more reported primary outcomes were not pre‐specified; outcomes of interest were reported incompletely and so could not be used; study failed to include results of a key outcome that would have been expected to have been reported);

• unclear risk of bias.

(6) Other bias (checking for bias due to problems not covered by (1) to (5) above)

For each included study, we described any important concerns we had about other possible sources of bias.

(7) Overall risk of bias

We made explicit judgements about whether studies were at high, unclear, or low risk of bias, according to the criteria given in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). With reference to (1) to (6) above, we assessed the likely magnitude and direction of the bias, and whether it was likely to impact on the findings. We explored the impact of the level of bias through, undertaking sensitivity analyses ‐ seeSensitivity analysis.

Assessment of the quality of the evidence using the GRADE approach

For this update, we assessed the quality of the evidence using the GRADE approach, as outlined in the GRADE handbook, in order to assess the quality of the body of evidence relating to the following outcomes, for the main comparison of cervical dilatation versus no dilatation (Schünemann 2013).

1. Postpartum haemorrhage: estimated blood loss greater than 1000 mL immediately or delayed after caesarean section

2. Need for blood transfusion: blood transfusion given during or within 24 hours after caesarean section

3. Drop in baseline haemoglobin (g/dL)

4. Secondary postpartum haemorrhage: late vaginal bleeding, within six weeks postpartum

5. Febrile morbidity: temperature of 38 degrees Celsius or higher on any two of the first 10 days postpartum, exclusive of the first 24 hours, of unknown causes.

6. Endometritis: febrile morbidity due to intrauterine infection, clinically diagnosed by fever, uterine tenderness, foul‐smelling discharge, or a combination

7. Uterine subinvolution: delayed or absent involution of the uterus during the postpartum period

We used GRADEpro GDT software to import data from Review Manager 5.3, to create the ’Summary of findings’ table (GRADEpro GDT). A summary of the intervention effect and a measure of quality for each of the above outcomes were produced using the GRADE approach. The GRADE approach uses five considerations (study limitations, consistency of effect, imprecision, indirectness, and publication bias) to assess the quality of the body of evidence for each outcome. The evidence can be downgraded from high quality by one level for serious (or by two levels for very serious) limitations, depending on assessments for risk of bias, indirectness of evidence, serious inconsistency, imprecision of effect estimates, or potential publication bias.

Dichotomous data

For dichotomous data, we presented results as summary risk ratio with 95% confidence intervals.

Continuous data

We used the mean difference, with 95% confidence intervals, if outcomes were measured in the same way between trials. In future updates, if applicable, we will use the standardised mean difference, with 95% confidence intervals, to combine trials that measure the same outcome, but used different methods.

Cluster‐randomised trials

Cluster‐randomised trials were eligible, but none were identified in this update. In future updates, if we identify any, we will include cluster‐randomised trials in the analyses along with individually randomised trials if there is little heterogeneity between the study designs, and the interaction between the effect of intervention and the choice of randomisation unit is considered to be unlikely. We will adjust the sample sizes of the cluster‐randomised trials using the methods described in the Cochrane Handbook for Systematic Reviews of Interventions, using an estimate of the intracluster correlation co‐efficient (ICC) derived from the trial (if possible), from a similar trial, or from a study of a similar population. If we use ICCs from other sources, we will report this and conduct sensitivity analyses to investigate the effect of variation in the ICC. We will also acknowledged heterogeneity in the randomisation unit, and perform a subgroup analysis to investigate the effects of the randomisation unit.

Cross‐over trials

This study design is not eligible for inclusion.