Reproductive and obstetric outcomes following frozen embryo transfer: letrozole combined with human menopausal gonadotropin versus hormone replacement cycle

Background This study aimed to compare reproductive and obstetric outcomes between frozen embryo transfer (FET) cycles using letrozole combined with human menopausal gonadotropin (HMG) for ovulation induction (OI) and hormone replacement therapy (HRT) for endometrial preparation. Methods A retrospective cohort study was conducted on 1,880 FET cycles from 2016 to 2024. Cycles were stratified into the OI group ( n = 902) and HRT group ( n = 978) based on the endometrial preparation protocol. The primary outcome was live birth rate (LBR). Secondary outcomes included clinical pregnancy rate (CPR) and obstetric complications. Exploratory subgroup analyses were performed based on ovulatory status (normal ovulation vs. ovulation disorders) and age (