Abstract
BACKGROUND: This study aimed to investigate the obstetric and perinatal outcomes of singleton deliveries following frozen embryo transfer (FET) cycles using different endometrial preparation methods. METHODS: We analyzed data on 44,118 singleton pregnant women who underwent in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI), resulting in delivery or abortion, from the South Korean National Health Insurance Service database. Stratification was based on the type of embryo transfer, viz. fresh embryo transfer and FET cycles, using International Classification of Diseases (Tenth Revision) diagnostic codes, national procedural codes, and prescription medication data within the IVF/ICSI pregnancy cohort. FET was subcategorized into artificial cycle-FET (AC-FET), natural cycle-FET (NC-FET), and stimulated cycle-FET (SC-FET) for comparative analyses of the pregnancy, obstetric, and perinatal outcomes. RESULTS: AC-FET was associated with higher risks of hypertensive disorders of pregnancy, preeclampsia, placenta accreta, and postpartum hemorrhage compared with NC-FET; the risk of macrosomia showed no significant differences. SC-FET was associated with a lower risk of miscarriage and higher rate of term birth beyond 37 weeks compared with NC-FET. However, SC-FET was associated with elevated risks of gestational hypertension and postpartum hemorrhage when compared to NC-FET. CONCLUSION: The rate of adverse obstetric and perinatal outcomes was higher in AC-FET compared to NC-FET, highlighting NC-FET as a valuable option owing to better maternal and fetal safety. In cases where NC-FET is not feasible, SC-FET presented as a favorable alternative, exhibiting lower miscarriage rates than NC-FET and better obstetric outcomes than AC-FET.