Caesarean section at term and the risk of preterm birth in subsequent pregnancy: a longitudinal linked national cohort study

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.