The association between prior cesarean section and subsequent in vitro fertilization outcomes in women undergoing autologous frozen thawed single euploid embryo transfer

Abstract Background Rates of cesarean section continue to increase worldwide. Previous work suggests an association between prior cesarean section and reduced fertility in natural and in vitro fertilization treatment cycles. To our knowledge, there is no published research exploring the relationship between a prior cesarean section and clinical outcomes after in vitro fertilization and subsequent frozen thawed euploid single embryo transfer. Objective This study aimed to investigate the relationship between prior mode of delivery and subsequent pregnancy outcomes in patients undergoing frozen thawed euploid single embryo transfer after in vitro fertilization. Study Design A retrospective cohort study was performed at a single academic fertility center from January 2012 to April 2020. All women with a history of a live birth undergoing autologous frozen thawed euploid single embryo transfer were identified. Cases included patients with a single prior cesarean section; controls included patients with a single prior vaginal delivery. Only the first embryo transfer cycle was included. The primary outcome was implantation rate. Secondary outcomes included ongoing pregnancy/live birth rate, biochemical pregnancy rate, and clinical miscarriage rate. Results A total of 525 patients met inclusion criteria and were included in analysis. Patients with a prior cesarean section had a higher BMI (24.5 + 4.5 vs 23.4 + 4.1, p=0.004) than those in the vaginal delivery cohort; demographic data were otherwise similar. In univariate analysis, the implantation rate was significantly lower in patients with a prior cesarean section (111/200 (55.5%) vs 221/325 (68.0%), p=0.004). After adjusting for relevant covariates, prior cesarean section was associated with 48% lower odds of implantation (aOR 0.52, 95% CI 0.34-0.78, p =0.002). Additionally, after adjusting for the same covariates, prior cesarean section was significantly associated with 39% lower odds of ongoing pregnancy/live birth (aOR 0.61, 95% CI 0.41-0.90, p=0.01). There were no differences in biochemical pregnancy rate or clinical miscarriage rate. Conclusions This is the first study to demonstrate a significant reduction in implantation and ongoing pregnancy/live birth associated with a prior cesarean section in patients undergoing a euploid embryo transfer. Our work stresses the importance of reducing primary cesarean section rates on a national level and elucidating the mechanisms behind substantially lower implantation rates after cesarean section.