First birth Caesarean section and subsequent fertility: a population-based study in the USA, 2000-2008.

STUDY QUESTION: Is first birth Caesarean delivery associated with a lower likelihood of subsequent childbearing when compared with first birth vaginal delivery?

SUMMARY ANSWER: In this study of US women whose first delivery was in 2000, those who had a Caesarean delivery were less likely to have a subsequent live birth than those who delivered vaginally.

WHAT IS ALREADY KNOWN: Some studies have reported lower birth rates subsequent to Caesarean delivery in comparison with vaginal delivery, while other studies have reported no difference.

STUDY DESIGN, SIZE, DURATION: We conducted a retrospective cohort study of 52 498 women who had a first singleton live birth in the State of Pennsylvania, USA in 2000 and were followed to the end of 2008 via Pennsylvania birth certificate records to identify subsequent live births during the 8- to 9-year follow-up period.

PARTICIPANTS/MATERIALS, SETTING, METHODS: Birth certificate records of first singleton births were linked to the hospital discharge data for each mother and newborn, and linked to all birth certificate records for each mother's subsequent deliveries which occurred in 2000 to the end of 2008. Poisson regression models were used to evaluate the association between first birth factors and whether or not there was a subsequent live birth during the follow-up period.

MAIN RESULTS AND THE ROLE OF CHANCE: Over an average of 8.5 years of follow-up, 40.2% of women with a Caesarean first birth did not have a subsequent live birth, compared with 33.1% of women with a vaginal first birth (risk ratio (RR): 1.21, 95% confidence interval (CI): 1.18-1.25). Adjustment for the demographic confounders of maternal age, race, education, marital status and health insurance coverage attenuated the RR to 1.16 (95% CI: 1.13-1.19). Specific pregnancy and childbirth-related complications associated with not having a subsequent live birth included diabetes-related disorders, abnormalities of organs and soft tissues of the pelvis, fetal abnormalities, premature or prolonged rupture of membranes, hypertensive disorders, amnionitis, fetal distress and other maternal health problems. However, adjustment for the pregnancy and childbirth complications had little effect on the RR of not having a subsequent live birth (RR = 1.15, 95% CI: 1.11-1.19).

LIMITATIONS, REASONS FOR CAUTION: We were unable to distinguish between women who did not have a subsequent live birth and those who moved out of the state, which may have introduced a selection bias if those who had Caesarean births were more likely to emigrate than those who delivered vaginally. In addition we were unable to measure pre-pregnancy body mass index, weight gain during pregnancy and prior infertility, which would have been helpful in our efforts to reduce selection bias.

WIDER IMPLICATIONS OF THE FINDINGS: The results of this study provide further corroboration of previous studies that have reported reduced fertility subsequent to Caesarean section in comparison with vaginal delivery.

STUDY FUNDING/POTENTIAL COMPETING INTERESTS: This study was funded by the US National Institute of Child Health and Human Development (NICHD, R01-HD052990). No competing interests are declared.