Pretreatment With a Long-acting GnRH Agonist in Early Follicular Phase Increases Clinical Pregnancy Rate in Frozen-thawed Embryo Transfer Cycles

Abstract Background: It is controversial whether gonadotropin-releasing hormone agonist (GnRHa) pretreatment can benefit the pregnancy outcomes in frozen-thawed embryo transfer (FET) cycles. In most of studies, GnRHa was administered during the mid-luteal phase for pretreatment. Few studies focus on FET cycles with GnRHa administered in early follicle phase.Methods: The retrospective cohort study was conducted in a university-affiliated IVF center. 630 patients in the GnRHa FET group and 1141 patients in the hormone replacement treatment (HRT) FET without GnRHa group from October 2017 to March 2019 were included. The menstruation cycle of these patients was irregular. Results: There were no differences observed between the two groups in patient’s characteristics. However, the GnRHa FET group showed a higher percentage of endometrium with triple line pattern (94.8% vs 89.6%, p<0.001) on the day of progesterone administration, and an increased implantation rate (34.7% vs 30%, p<0.01), biochemical pregnancy rate (60.6% vs 54.3%, p = 0.009), and clinical pregnancy rate (49.8% vs 43.3%, p = 0.008), as compared to that in the HRT FET cycles with similar endometrial thickness, ectopic pregnancy rate, and early miscarriage rate. Binary logistic regression analysis showed the GnRHa FET group to be associated with an increased chance of clinical pregnancy rate compared with HRT FET without GnRHa group (P=0.014, odds ratio [OR] 1.30, 95% confidence interval [CI] 1.06-1.61).Conclusions: Pretreatment with a long-acting GnRHa in early follicular phase can improve the clinical outcome of the FET cycles. However, further randomized control trials (RCTs) will be needed to verify these results.