Impact of time interval from cesarean delivery to frozen embryo transfer on reproductive and neonatal outcomes

Objective: To evaluate differences in reproductive and neonatal outcomes on the basis of the time interval from cesarean delivery to subsequent frozen embryo transfer (FET). Design: Retrospective cohort. Setting: Multicenter fertility practice. Patients: Women undergoing autologous elective single embryo transfer FET after prior cesarean delivery. Intervention: Time from prior cesarean delivery to subsequent FET. Results: A total of 6,556 autologous elective single embryo transfer FET cycles were included. Frozen embryo transfer cycles were divided into eight groups on the basis of the time interval from prior cesarean delivery to subsequent FET in months. A secondary analysis was then performed with time as a continuous variable. The proportion of LBs did not differ significantly across all time interval groups and over continuous time (range: 40.0%-45.6%). The mean gestational age at the time of delivery did not significantly differ as the time between prior cesarean delivery and subsequent FET increased (range: 37.3-38.4). When time was evaluated continuously, the proportion of preterm births was higher with a shorter time between cesarean delivery and subsequent FET. The mean birth weight ranged from 3,181-3,470g, with a statistically significant increase over time. However, the proportions of extremely low birth weight, very low birth weight, and low birth weight did not significantly differ. Conclusion: There were no significant differences in reproductive outcomes on the basis of the time interval from cesarean delivery to FET, including LB. The proportion of preterm deliveries decreased with a longer time between cesarean delivery and FET. Differences in mean neonatal birth weight were not clinically significant because the proportion of low birth weight neonates was not significantly different over time. Although large, this sample cannot address all outcomes associated with short interpregnancy intervals, particularly rarer outcomes such as uterine rupture. When counseling patients, the timing of FET after cesarean delivery must be balanced against the risks of increasing maternal age on reproductive and neonatal outcomes.