Abstract: Objective: To investigate the effects of gonadotrophin releasing hormone agonist (GnRHa) pretreatment on the outcomes of frozen-thawed embryo transfer (FET) cycles and endometrial receptivity for the women with recurrent implantation failure. Methods: A total of 131 women undergoing FET cycles in the reproductive medical center of the First Affiliated Hospital of Guangxi Medical University and the People′s Hospital of Liuzhou with a history of recurrent implantation failure (≥2 times) were enrolled in this retrospective study from January 2014 to August 2015. According to the protocols of endometrial preparation, those women were grouped into two groups: the group A received only hormone replacement treatment (HRT) for endometrial preparation (69 cycles)，and the group B received GnRHa down-regulation pretreatment before HRT (62 cycles). Meanwhile，the 48 patients in group B who had received HRT for endometrial preparation previous FET cycle (sub-groups) were also performed the self-control comparison. Results: There were no statistical differences in the age, duration of infertility, basal endocrine level, body-mass index (BMI), endometrial thickness, number of embryo transferred, number of good-quality embryo, good-quality embryo rate, early abortion rate between the two groups (P＞0.05)，whereas the clinical pregnancy rate and implantation rate as well as the proportion of pattern A endometrial blood flow in group B were significantly higher than those in group A (P＜0.05). The self-control comparison showed that the proportion of pattern A endometrial blood flow was significantly higher in those cycles with GnRHa down-regulation than that in cycles with only HRT (P＜0.05)，and that there were no significant differences in endometrial thickness and the good-quality embryo rate between the two sub-groups (P＞0.05). Conclusions: GnRHa down-regulation pretreatment before HRT can significantly improve the endometrial receptivity and clinical pregnancy rate for the patients with recurrent implantation failure in FET cycle.

Key words: Embryo transfer, Gonadotropin-releasing hormone, Hormone replacement therapy, Endometrium, Pregnancy rate