Association Between Mode of First Delivery and Subsequent Fecundity and Fertility

Importance More than 20% of births globally are by cesarean delivery, including more than 30% in the US. Prior studies have reported lower rates of childbearing after cesarean delivery, but it is not clear if this is due to maternal choice or lower conception rates. Objective To investigate the association between mode of first delivery and subsequent conceptions and live births. Design, Setting, and Participants The First Baby Study was a multicenter prospective cohort study of women aged 18 to 35 years with singleton pregnancies, enrolled and interviewed before first childbirth, who delivered in Pennsylvania from 2009 to 2011 and were followed up for 36 months after delivery (until April 2014). Data analysis for this study took place between May and July 2019 and in January 2020. Exposures Mode of first delivery (cesarean or vaginal). Main Outcomes and Measures Rates of subsequent conceptions and live births. Discrete-time Cox proportional hazard regression models were used to compare the rate of subsequent conception (vaginal vs cesarean) among those who completed the 36-month survey, accounting for reported months of unprotected intercourse during the follow-up period and adjusting for relevant covariates. A log binomial regression was used to compare the age-adjusted rate of subsequent live birth (vaginal vs cesarean) among those who completed the 36-month survey. Results The study population consisted of 2423 women who were retained to the 36-month survey (mean [SD] age at baseline was 27.2 [4.4] years and 712 [29.4%] delivered by cesarean). There were 2046 women who had unprotected intercourse during the follow-up period, 2021 of whom provided data on months of unprotected intercourse. Cesarean delivery was associated with lower rates of conception after unprotected intercourse during the follow-up period (413 of 599 [68.9%]) compared with vaginal delivery (1090 of 1422 [76.7%]) (adjusted hazard ratio, 0.85; 95% CI, 0.74-0.96). Cesarean delivery was also associated with reduced likelihood of a subsequent live birth (305 women [42.8%]) compared with vaginal delivery (857 women [50.1%]), with an age-adjusted risk ratio of 0.83 (95% CI, 0.75-0.92). Conclusions and Relevance In the 3 years following first childbirth, women who delivered their first child by cesarean had lower rates of conception after unprotected intercourse, and fewer of these women had a second child than those who delivered vaginally. Question Is cesarean delivery at first childbirth associated with a lower rate of subsequent conception compared with vaginal delivery? Findings In this cohort study of 2423 women, first childbirth by cesarean delivery was associated with a lower rate of conception after unprotected intercourse when compared with conception rates of women after vaginal delivery. These results remained significant after controlling for relevant covariates. Meaning These findings suggest that women who deliver their first child by cesarean delivery may be less likely to conceive a second child in the 3 years following first delivery than women who deliver their first child vaginally. This cohort study examines the association of first childbirth by cesarean vs vaginal delivery with rates of subsequent conceptions and live births among US women.