The endometrial preparation protocol of gonadotropin-releasing hormone agonist with hormone replacement therapy can improve the reproductive outcomes in women under FET cycles: a retrospective study.

Background: Hormone replacement therapy (HRT) is the most commonly used method for the endometrial preparation before frozen embryo transfer (FET), but whether pretreatment with gonadotropin-releasing hormone agonist (GnRH-a) could improve live birth rates remains controversial. This study aims at examining the efficacy of GnRH-a with HRT in the preparation of the endometrium during FET cycles. Methods: : The retrospective cohort research of clinical files between January 2016 and October 2020. A total of 6,034 infertile women received HRT as endometrial preparation during the FET cycle at two Reproductive Medicine Centers. Based on whether or not GnRH-a was pretreatment, the study was divided into two groups: HRT cycles consisted of 2404 cycles as the HRT group, and HRT with GnRH-a cycle consisted of 2402 cycles as the GnRHa-HRT group. The primary outcome measure was the live birth rate. Secondary endpoints included the rate of implantation, biochemical pregnancy, clinical pregnancy, miscarriage, biochemical abortion, ectopic pregnancy, multiple pregnancy, preterm delivery, term delivery, low birth weight infant and fetal macrosomia as well as birth weight. Result: (s) Among 4,806 participants, baseline characteristics were similar between the two groups. Compared with the HRT group, HRT pretreatment with GnRH-a significantly increased pregnancy outcomes of FET, such as live birth rates (44.5% VS. 38.1%; P=0.000, OR 1.30,95%CI 1.16-1.46), implantation rate (37.9%VS. 33.0%; P=0.000; OR 1.24,95%CI 1.13-1.35). And the GnRHa-HRT group and the HRT group had similar rates of pregnancy loss (25.1% VS. 27.8%; P=0.107, OR 0.87,95%CI 0.74-1.03). GnRHa pretreated with HRT resulted in an increased risk of fetal macrosomia (20.9% VS. 17.3%; P=0.025, OR 1.264,95%CI 1.03-1.55). The other pregnancy complications such as ectopic pregnancy, multiple pregnancies and preterm delivery were no statistical significance between the two protocols. Conclusion: (s) Pretreatment with GnRH-a can improve the reproductive outcomes and may increase the risk of pregnancy with macrocephaly, in women receiving HRT in endometrial preparation under FET cycles.