Abstract: Objective · To explore the factors affecting the pregnancy outcome of frozen-thawed embryo transfer (FET) in endometriosis (EMT) patients into provide reference for the clinical selection of FET strategies. Methods · A total of 329 EMT patients who received blastocyst FET at the Reproductive Medicine Center, Department of Obstetrics & Gynecology, The 900th Hospital of the Joint Logistics Support Force, PLA, Jan. 2015 to Dec. 2017 were analyzed retrospectively. The patients were divided into three groups according to endometrial preparation protocols, ages, and endometrial thickness on the day of progesterone conversion, respectively.endometrial preparation protocols, the three groups included gonadotropinreleasing hormone agonist (GnRH-a) down-regulation+ hormone replacement therapy (HRT) group (GnRH-a+HRT group, A1 group, n138), HRT group (B1 group, n52), and natural cycle (NC) group (C1 group, n139).ages, the three groups included <30 years old group (A2 group, n109), 30-35 years old group (B2 group, n161), and >35 years old group (C2 group, n59).endometrial thickness on the day of progesterone conversion, the three groups included <9 mm group (A3 group, n111), 9-12 mm group (B3 group, n181), and >12 mm group (C3 group, n37). The differences in pregnancy outcomes among EMT patients with blastocyst FET were compared under different grouping factors. Results · The endometrium of A1 group was significantly thicker than thatof B1 group (P0.041), the implantation rate and clinical pregnancy rate of B1 group weresignificantly higherthanthose of C1 group (P0.000, P0.003). Compared with A1 group, the implantation rate of B1 group was significantly higher (P0.023), while it was significantly lower in group C1 (P0.027). The abortion rate of A2 group was significantly higher than that of B2 group (P0.007). Compared with A3 group, the implantation rate of B3 group was significantly higher (P0.041), while it was significantly lower in C3 group (P0.026). Conclusion · HRT endometrial preparation protocol for EMT patients with blastocyst FET can improve the implantation rate and clinical pregnancy rate, and reduce the abortion rate and ectopic pregnancy rate, which maybe an economicalandefficient endometrial preparation protocol inclinical.

Key words: endometriosis (EMT), frozen-thawed embryo transfer (FET), endometrial preparation, gonadotropin-releasing hormone agonist (GnRH-a), down-regulation, hormone replacement therapy (HRT)