GnRH-a Pretreatment Doses and Frozen-Thawed Blastocyst Transfer Outcomes in PCOS Patients: A Retrospective Cohort Study.

Objective: To evaluate the effects of GnRH-a pretreatment with 1.5 mg or 3.75 mg, in combination with hormone replacement therapy (HRT), on pregnancy outcomes in women with polycystic ovary syndrome (PCOS) undergoing frozen embryo transfer (FET). Methods: We conducted a retrospective analysis of 555 FET cycles in PCOS patients treated at our center between July 2022 and June 2024. Based on endometrial preparation regimens, participants were allocated into three groups: HRT alone, GnRH-a (1.5 mg) + HRT, and GnRH-a (3.75 mg) + HRT. Baseline characteristics and pregnancy outcomes were compared among the groups. Multivariable logistic regression was used to adjust for potential confounders. Results: Baseline characteristics were comparable among groups in age, duration of infertility, body mass index (BMI), endometrial thickness on the start day, estradiol (E2) and luteinizing hormone (LH) on the start day, endometrial thickness on the day of embryo transfer (ET), E2 on the ET day, and days of estradiol valerate administration (all P > 0.05). The proportion of double-embryo transfer cycles was higher in the 1.5 mg GnRH-a + HRT group than in the other two groups (P < 0.001). Pregnancy outcomes, including implantation rate (54.17% vs 46.81% vs 56.73%), clinical pregnancy rate (57.68% vs 57.43% vs 63.70%), early pregnancy loss rate (11.41% vs 13.24% vs 9.30%), and ectopic pregnancy rate (1.09% vs 0.00% vs 1.16%), did not differ significantly among groups (P > 0.05). Multivariable analysis identified the number of embryos transferred as the only factor significantly associated with pregnancy outcome (P < 0.001). Conclusion: GnRH-a pretreatment at either 1.5 mg or 3.75 mg did not confer a clear benefit over HRT alone in PCOS patients undergoing FET. The number of embryos transferred remains the primary determinant of pregnancy outcome. Larger prospective studies are warranted to validate these findings.