Endometrial preparation methods prior to frozen embryo transfer: a retrospective cohort study comparing true natural cycle, ovulation induction, hormone replacement treatment and GnRHa pretreatment

To compare pregnancy outcomes of four endometrial preparation methods prior to frozen embryo transfer (FET). A total of 3,030 programmed cycles were analyzed: 302 with natural cycle (NC), 131 with ovulation induction (OI), 1,078 with hormone replacement treatment (HRT), and 1,519 with GnRHa pretreatment (GnRHa + HRT). Primary outcomes investigated were positive human chorionic gonadotropin (hCG), chemical pregnancy, clinical pregnancy, abortion, and live birth. Additionally, the impact of age, body mass index (BMI), embryo number, high-quality embryo, and endometrial thickness on pregnancy outcomes were analyzed. The positive hCG rates for NC, OI, HRT, and GnRHa + HRT groups were 63.4%, 62.6%, 68.3%, and 71.7%, respectively (P = 0.004). Clinical pregnancy rates were 50.4%, 54%, 57.5%, and 61.8%, respectively (P = 0.004). Live birth rates were 38.2%, 45%, 46.5%, and 50.9%, respectively (P = 0.007). No significant differences were found in abortion and chemical pregnancy rates among the four protocols. NC showed significantly higher positive hCG (p = 0.044), live birth (p = 0.005), and clinical pregnancy rates (p = 0.010) compared to other methods. Compared to HRT, GnRHa + HRT displayed significantly higher live birth (p = 0.027) and clinical pregnancy rates (p = 0.027). Multiple logistic regression showed that the number of embryos and high-quality embryos increased HCG positivity, clinical pregnancy, and live birth rates, while age reduced these rates. BMI increased the abortion rate, and endometrial thickness increased the live birth rate. Chemical pregnancy was unaffected by these factors. NC offers improved outcomes compared to other methods. Additionally, specific factors such as embryo quality and embryo number significantly influence pregnancy outcomes. Not applicable.