Reproductive and pregnancy outcomes following embryo transfer in women with previous cesarean section: A systematic review and meta-analysis.

INTRODUCTION Cesarean section affects subsequent spontaneous pregnancies because of implantation issues. However, its impact on post-embryo transfer pregnancies is still debated. This review aimed to evaluate the impact of a previous cesarean section on fertility and pregnancy outcomes of women undergoing fresh or frozen embryo transfer. MATERIAL AND METHODS MEDLINE, Scopus, ClinicalTrials.gov, Scielo, EMBASE, Cochrane Library at the CENTRAL, and LILACS were searched from inception to February 2021. Studies were included if they evaluated reproductive or pregnancy outcomes after fresh or frozen embryo transfer in infertile women with a previous cesarean section relative to women with a previous vaginal delivery. Random-effect meta-analyses to calculate risk ratio (RR) or mean differences with 95% confidence intervals (CI) followed by subgroup analysis for fresh and frozen embryo transfer were performed. Risk of bias and quality assessment were conducted using Newcastle-Ottawa scale and GRADE criteria. The review was registered in the International Prospective Register of Systematic Reviews (CRD42021226297). RESULTS Ten studies, with data provided for 13 696 participants, were eligible. For embryo transfers after cesarean section, compared with vaginal delivery, there was a significant reduction of the live birth rate (RR 0.88, 95% CI 0.79-0.99) and biochemical pregnancy rate (RR 0.89, 95% CI 0.82-0.96). No statistically significant differences were found for clinical pregnancy rate (RR 0.92, 95% CI 0.84-1.02), ectopic pregnancies (RR 1.00, 95% CI 0.68-1.46), pregnancy loss (RR 1.05, 95% CI 0.94-1.18), multiple pregnancies (RR 0.80, 95% CI 0.63-1.02), stillbirths (RR 0.86, 95% CI 0.27-2.69), birth defects (RR 1.71, 95% CI 0.49-5.96) or birthweight (mean difference 46.82, 95% CI -40.16 to 133.80). Subgroup analysis revealed an increased risk for preterm birth in post-cesarean section fresh embryo transfer pregnancies (RR 1.59, 95% CI 1.16-2.19). CONCLUSIONS Low-grade evidence shows that post-embryo transfer pregnancies in infertile women who had a previous cesarean delivery result in reduced biochemical pregnancy and live birth rates relative to women with a previous vaginal delivery. An increased risk for preterm birth is notable in post-fresh embryo transfer pregnancies.