OBJECTIVE: To probe into the effects of tamoxifen combined with human chorionic gonadotropin（ HCG） on endometrial receptivity in patients with repeated implantation failure（ RIF） during freeze-thaw cycles.METHODS: The clinical data of 188 patients with RIF（ ≥3 times） undergoing freeze-thaw embryo transfer in our hospital from Jul. 2017 to Jun. 2019 were retrospectively analyzed. All patients were divided into the observation group（ n = 105） and the control group（ n = 83） according to different endometrial preparation schemes. The observation group was given tamoxifen combined with HCG intrauterine infusion

while the control group received letrozole combined with HCG intrauterine infusion. Differences of endometrial thickness and subendometrial blood flow[pulsatility index（ PI）

resistance index（ RI） ]

endometrial blood flow type

hormone levels on HCG day and transplantation day [luteinizing hormone（ LH）

estradiol（ E2） and progesterone]levels and pregnancy outcomes of two groups were compared. RESULTS: On transplantation day

the endometrial thickness of two groups increased significantly compared with that before ovulation induction

and the observation group was significantly larger than the control group

with statistically significant difference（ P < 0. 05）. The PI and RI of two groups were lower than those before ovulation induction

and the observation group was significantly lower than the control group

with statistically significant difference（ P < 0. 05）. The proportion of type A endometrial blood flow in the observation group was80. 95%（ 85/105）

significantly higher than 40. 96%（ 34/83） in the control group

with statistically significant difference（ P < 0. 05）. E2 on HCG day and E2 on transplantation day in the observation group were significantly higher than those in the control group

and LH on HCG day was lower than that in the control group

the differences were statistically significant（ P < 0. 05）. The implantation rate and clinical pregnancy rate of the observation group were significantly higher than those of the control group

with statistically significant difference（ P < 0. 05）.CONCLUSIONS: Tamoxifen combined with HCG can effectively increase endometrial thickness

improve endometrial receptivity and pregnancy rate in RIF patients during freeze-thaw cycles.