Spontaneous preterm birth risk after caesarean section at full dilatation in the first birth compared to all other births: A systematic review and meta-analysis of observational studies.

Caesarean section performed at full dilation (CSfd) has been associated with higher risk of spontaneous preterm birth (sPTB) in subsequent pregnancies. This review aimed to investigate the impact of a CSfd on subsequent pregnancies compared to all other modes of birth.. To compare the risk of sPTB in a subsequent pregnancy following CSfd versus any other mode of birth in the index pregnancy. MEDLINE, EMBASE, PubMed, Cochrane Library and Google Scholar were searched electronically following PRISMA guidance. Eligible observational studies included women with at least two consecutive singleton births, where the first birth was at term (≥37 weeks). The exposure was CSfd versus any other birth mode in the index pregnancy, and the outcome was sPTB in the subsequent pregnancy. Two authors independently extracted data and assessed quality using the Newcastle-Ottawa Scale. Meta-analyses were performed using random effects models to synthesise pooled odds ratios (OR) for sPTB using RevMan software. Fourteen studies were included, pooling data from 708,102 women (1998-2022). Compared against any other mode of birth, CSfd was associated with a significantly increased risk of sPTB (OR 1.91 [95% confidence interval (CI) 1.79, 2.04]). Subgroup analyses showed doubled the odds of sPTB < 34 weeks gestation after CSfd (OR 2.90 [95% CI: 2.49, 3.38]). Risk of bias was low in the majority of included studies. We have demonstrated a clear relationship between CSfd and subsequent sPTB. This information may help to inform surveillance pathways, such as cervical length screening in future pregnancies.