Mode of delivery and subsequent reproductive patterns. A national follow-up study.

OBJECTIVE To investigate associations between mode of delivery and subsequent reproductive outcomes. DESIGN Cohort study. POPULATION Women with term singleton live births from 1987 to 2009. SETTING Denmark, birth registration data. METHODS Women with a first singleton delivery after 37 weeks were followed until the end of 2010, from a first birth to include subsequent live births. We used Cox's proportional hazards model stratified by parity to compare the likelihood for subsequent delivery according to mode of delivery at first and later births, estimating maternal age effects and lag time to next delivery. MAIN OUTCOME MEASURE Likelihood of a subsequent live-born child by previous delivery mode. RESULTS We identified 642,052 women with a first delivery. Compared with women with a non-instrumental vaginal delivery, delivering a child by elective cesarean section implied a 23% (95% CI 0.76-0.787) decreased likelihood for subsequent delivery. Emergency cesarean section meant 16% fewer (95% CI 0.84-0.85), and vaginal instrumental delivery 4% fewer subsequent deliveries (95% CI 0.95-0.96). Hazard ratios were largely unchanged after controlling for parity and year of birth. Small age-trends were seen, with hazard ratios affected by maternal age at birth. Delivery mode at first birth affected marginally the time lag until next birth. CONCLUSIONS Fecundity, measured as likelihood of a successive live-born child, varied with mode of delivery at the first and also subsequent births. A first or later delivery by cesarean section implied decreased likelihood of subsequent delivery compared with women with a first vaginal birth.