Risk of preterm birth after prior term cesarean

Objective To determine the risk of overall preterm birth (PTB) and spontaneous PTB in a pregnancy after a caesarean section (CS) at term. Design Longitudinal linked national cohort study. Setting The Dutch Perinatal Registry (1999-2009). Population 268 495 women with two subsequent singleton pregnancies were identified. Methods A cohort study based on linked registered data from two subsequent pregnancies in The Netherlands. Main outcome measures The incidence of overall PTB and spontaneous PTB with subgroup analysis on gestational age at first delivery and type of CS (planned or unplanned). Results Of 268 495 women with a singleton first pregnancy who delivered at term, 15.76% (n = 42 328) had a CS. The incidence of PTB in the second pregnancy was 2.79% (n = 1182) in women with a previous CS versus 2.46% (n = 5570) in women with a previous vaginal delivery (adjusted odds ratio [aOR] 1.14, 95% confidence interval [CI] 1.07-1.21). This increased risk is mainly driven by an increased risk of spontaneous PTB after previous CS at term (aOR 1.50, 95% CI 1.38-1.70). Analysis for type of CS compared with vaginal delivery showed an aOR on spontaneous PTB of 1.86 (95% CI 1.58-2.18) for planned CS and an aOR of 1.40 (95% CI 1.24-1.58) for unplanned CS. Conclusions CS at term is associated with a marginally increased risk of spontaneous PTB in a subsequent pregnancy. Tweetable abstract Caesarean section at term is associated with a marginally increased risk of spontaneous PTB in a subsequent pregnancy.