Perinatal outcomes are similar in programmed and modified natural frozen embryo transfer cycles

Research question: How do perinatal outcomes differ between programmed and modified fi ed natural frozen embryo transfer (FET) cycles? Design: A retrospective cohort study of 839 patients was undertaken at a university-affiliated fi liated fertility practice undergoing single blastocyst FET cycles between 2014 and 2020. The primary outcome measures were the incidence of ischaemic placental disease, small for gestational age (SGA), intrauterine growth restriction (IUGR), preterm delivery, birth weight, and mode of delivery. Results: When comparing programmed FET cycles with modified fi ed natural FET cycles, there was no increased risk of ischaemic placental disease [adjusted risk ratio (aRR) 0.83, 95% CI 0.61-1.14],- 1.14], IUGR (unadjusted RR 0.50, 95% CI 0.14-1.77),- 1.77), preterm delivery (aRR 1.11, 95% CI 0.72-1.70)- 1.70) or SGA (aRR 0.69, 95% CI 0.40-1.19).- 1.19). Patients in the programmed cohort had increased risk of caesarean delivery (aRR 1.32, 95% CI 1.10-1.59).- 1.59). These outcomes were unchanged when limited to patients undergoing their fi rst FET cycle. Conclusions: There are no differences in patient and neonatal clinical outcomes between programmed and modified fi ed natural FET cycles. The choice of FET protocol should remain a shared decision between patient and provider.