Research QuestionHow do perinatal outcomes differ between programmed and modified natural Frozen Embryo Transfer cycles? DesignWe performed a retrospective cohort study of 839 patients at a university-affiliated fertility practice undergoing single blastocyst FETs between 2014 and 2020. The primary outcome measures were the incidence of ischemic placental disease, small for gestational age, intrauterine growth restriction, preterm delivery, birthweight, and mode of delivery. ResultsWhen comparing programmed cycles to modified natural cycles, there was no increased risk of ischemic placental disease (adjusted risk ratio (aRR): 0.87; 95% confidence interval (CI): 0.64–1.17), IUGR (unadjusted RR: 0.50, 95% CI 0.14–1.77), or preterm delivery (aRR: 1.10, 95% 0.73–1.65), or SGA infants (aRR: 0.69, 95%: CI 0.40–1.19). Patients in the programmed cohort had an increased risk of cesarean delivery (aRR: 1.32, 95% CI: 1.10–1.59). These outcomes were unchanged when limited to patient undergoing their first cycles. ConclusionsThere are no differences in patient and neonatal clinical outcomes between programmed and modified natural FET cycles. The choice of FET protocol should remain a shared decision between patient and provider.