Abstract: A total of 29 trials were included in this review and 21 trials (17,276 women) provided data that could be included in an analysis. The quality of the trials was variable. 1. Non-closure of visceral and parietal peritoneum versus closure of both parietal layers Sixteen trials involving 15,480 women, were included and analysed, when both parietal peritoneum was left unclosed versus when both peritoneal surfaces were closed. Postoperative adhesion formation was assessed in only four trials with 282 women, and no difference was found between groups (risk ratio (RR) 0.99, 95% confidence interval (CI) 0.76 to 1.29). There was significant reduction in the operative time (mean difference (MD) -5.81 minutes, 95% CI -7.68 to -3.93). The duration of hospital stay in a total of 13 trials involving 14,906 women, was also reduced (MD -0.26, 95% CI -0.47 to -0.05) days. In a trial involving 112 women, reduced chronic pelvic pain was found in the peritoneal non-closure group. 2. Non-closure of visceral peritoneum only versus closure of both peritoneal surfaces Three trials involving 889 women were analysed. There was an increase in adhesion formation (two trials involving 157 women, RR 2.49, 95% CI 1.49 to 4.16) which was limited to one trial with high risk of bias.There was reduction in operative time, postoperative days in hospital and wound infection. There was no significant reduction in postoperative pyrexia. 3. Non-closure of parietal peritoneum only versus closure of both peritoneal layers The two identified trials involved 573 women. Neither study reported on postoperative adhesion formation. There was reduction in operative time and postoperative pain with no difference in the incidence of postoperative pyrexia, endometritis, postoperative duration of hospital stay and wound infection. In only one study, postoperative day one wound pain assessed by the numerical rating scale, (MD -1.60, 95% CI -1.97 to -1.23) and chronic abdominal pain d by the visual analogue score (MD -1.10, 95% CI -1.39 to -0.81) was reduced in the non-closure group. 4. Non-closure versus closure of visceral peritoneum when parietal peritoneum is closed. There was reduction in all the major urinary symptoms of frequency, urgency and stress incontinence when the visceral peritoneum is left unsutured. There was a reduction in operative time across all the subgroups. There was also a reduction in the period of hospitalisation post-caesarean section except in the subgroup where parietal peritoneum only was not sutured where there was no difference in the period of hospitalisation. The evidence on adhesion formation was limited and inconsistent. There is currently insufficient evidence of benefit to justify the additional time and use of suture material necessary for peritoneal closure. More robust evidence on long-term pain, adhesion formation and infertility is needed.

Plain-language summary: There are many ways of performing a caesarean section and the techniques used depend on a number factors including the clinical situation and the preference of the operator. The peritoneum is a thin membrane of cells supported by a thin layer of connective tissue, and during caesarean section these peritoneal surfaces have to be cut through in order to reach the uterus and for the baby to be born. Following a caesarean section, it has been standard practice to close the peritoneum by stitching (suturing) the two layers of tissue that line the abdomen and cover the internal organs, to restore the anatomy. It has however been suggested that peritoneal adhesions may be more likely rather than less likely when the peritoneum is sutured, possibly as a result of a tissue reaction to the suture material. This review of trials sought to address whether to routinely suture these thin layers of tissue or not after delivering a baby by caesarean section. Twenty-nine randomised controlled trials were identified, with differences in their methodological quality; 21 trials involving over 17,000 women contributing data to the review. Several minutes were saved when the peritoneum was not stitched, and with a shorter period of hospital stay in most of the women. Postoperative adhesion formation was assessed in only four trials with 282 women, and no difference was found when leaving both layers of peritoneum unclosed was compared with closure of both. Longer-term outcomes were not adequately assessed, particularly adhesion formation, subfertility and ease of other surgeries in later life. Although the methodological quality of trials was variable, the results were in general consistent between the trials of better and poorer quality. Further studies are needed to further assess all these outcomes.