The impact of first birth by cesarean delivery on subsequent reproductive outcomes-a population cohort study.

Abstract

Cesarean deliveries are one of the most common obstetric interventions globally. It is important all risks are fully understood. This study aimed to investigate the impact of first birth by cesarean delivery on subsequent reproductive outcomes. We conducted a retrospective cohort study of all women who gave birth to their first spontaneously conceived, singleton infant in Victoria, Australia from January 2005 to December 2015, with follow-up for second births until December 2017. The exposure was first birth by cesarean delivery, compared with vaginal birth. Primary outcomes included (1) a second live birth occurring within the study time frame and (2) conception via in vitro fertilization or other assisted reproductive technologies among those for whom a second birth was reported. Secondary outcomes included interpregnancy interval and miscarriage rates. Statistical analyses included Cox proportional hazards regression, Poisson regression, or quantile regression depending on the outcome. Outcomes were adjusted for maternal age (at both first and second pregnancy), Socio-Economic Indexes for Areas quintile at the time of pregnancy, preexisting hypertension, and preexisting diabetes. There were 298,241 women who met the inclusion criteria, of whom 184,061 (61.7%) had both their first and second birth during the 12-year study period. A total of 205,164 had a vaginal birth and 93,077 gave birth by cesarean delivery. Having a first birth by cesarean delivery was associated with an 11% reduction in the likelihood of having a second live birth (adjusted hazard ratio, 0.89; 95% confidence interval, 0.88-0.90). Among the cohort reporting a second live birth, there was a 28% increase in the use of in vitro fertilization for conception among those who had a prior cesarean delivery (adjusted risk ratio, 1.28; 95% confidence interval, 1.15-1.43) and a 28% increase in the probability of any assisted reproductive technology use (adjusted risk ratio, 1.28; 95% confidence interval, 1.18-1.40). No difference in miscarriage rates was observed (adjusted risk ratio, 1.01; 95% confidence interval, 0.98-1.03). First birth by cesarean delivery was associated with an 11% reduced likelihood of a second live birth within the 12-year study period and a 28% increase in the use of assisted reproductive technologies to achieve a second birth. Factors leading to a cesarean delivery may also be associated with subsequent reproductive outcomes and warrant further study.