Second stage cesarean section and the risk of preterm birth in subsequent pregnancies.

Objective: To evaluate the risk of spontaneous preterm birth on subsequent pregnancies after second stage cesarean section.

Methods: This is a retrospective cohort study. Women were included if they had their two consecutive births in Toulouse University Hospital in the study period. The first birth was a singleton livebirth at term (≥37 weeks of gestation), divided in three categories according to the mode of delivery: vaginal delivery (group A), cesarean section before the second stage of labor (group B), cesarean section during the second stage of labor (group C). The subsequent pregnancy was the first subsequent pregnancy, conducted after 16 weeks of gestation. The primary outcome was spontaneous preterm birth in the subsequent pregnancy, defined as delivery before 37 weeks of gestation. Secondary endpoints included preterm rupture of membranes in the subsequent pregnancy.

Results: Between 2003 and 2018, 7776 women (84.7%) in group A, 1263 (13.8%) in group B and 143 (1.5%) in group C were included. The adjusted odds ratio of spontaneous preterm birth before 37 weeks of gestation after second stage cesarean section was 2.4 (group C vs group A + B, 95% confidence interval: 1.2-4.8), P = 0.01). The rate of preterm rupture of membranes was also significantly higher in group C (6% vs 2% in group A, P = 0.009, 6% vs 3% in group B, P= 0.05) with OR = 3.0 (group C vs group A + B, 95% CI: 1.55-6.16, P < 0.001).

Conclusion: History of term second stage of labor cesarean section is an independent risk factor for spontaneous preterm birth and for preterm rupture of membrane in the subsequent pregnancy.