Mode of delivery and preterm birth in subsequent births: A systematic review and meta-analysis.

Preterm birth continues to be an important problem in modern obstetrics and a large public health concern and is related to increased risk for neonatal morbidity and mortality. The aim of this study was to evaluate the data in the literature to determine the relationships between mode of delivery (cesarean section and vaginal birth) in the first pregnancy and the risk of subsequent preterm birth from a multi-year population based cohorts (PROSPERO registration number: 42018090788). Five electronic databases were searched. Observational studies that provided mode of delivery and subsequent preterm birth were eligible. Ten cohort studies, involving 10333501 women, were included in this study. Compared with vaginal delivery, women delivering by previous cesarean section had a significantly higher risk of preterm birth in subsequent births (RR 1.10, 95%CI 1.01-1.20). After adjusting confounding factors, there was still statistical significance (aRR 1.12, 95%CI 1.01-1.24). However, both before and after adjustment, there was no difference among very preterm birth (RR 1.14, 95%CI 0.90-1.43; aRR 1.16, 95%CI 0.80-1.68; respectively). To the best of our knowledge, this is the first systematic review and meta-analysis that suggests previous cesarean section could increase the risk of preterm birth in subsequent pregnancies. The result could provide policy makers, clinicians, and expectant parents to reduce the occurrence of unnecessary cesarean section.