Abstract: Objective：To investigate the effect of human chorionic gonadotropin (hCG) injected on the transfer day on the pregnancy outcomes of frozen-thawed embryo transfer (FET) cycles. Methods：A total of 1636 FET cycles from May 2015 to August 2017 were analyzed retrospectively. These cycles were divided into the hCG group (1 084 cycles) and the control group (552 cycles). The pregnancy outcomes were compared between the two groups. Results：The baseline characteristics of age, body mass index, infertile duration, basic FSH level, number of embryos transferred and endometrial thickness on the transfer day were similar in the two groups (P＞0.05). There were no significant differences in the clinical pregnancy outcomes between the two groups, including the clinical pregnancy rate, embryo implantation rate, ectopic pregnancy rate, abortion rate and live birth rate(P＞0.05). The subgroup analysis, based on the transferred embryos at the cleavage stage, morula stage and blastocyst stage, found that there was no significant difference in the outcome of pregnancy(P＞0.05). Logistic multivariate regression analysis showed that age, the number of transferred embryos and transferred high-quality embryos were the factors influencing clinical pregnancy, and that age was an independent factor influencing the live birth rate. The live birth rate in those aging women was lower. Conclusions: HCG injected on the transfer day of FET cycles has no significant effect on the clinical pregnancy outcomes. Age is an important factor of the pregnancy outcomes.

Key words: Embryo transfer, Chorionic gonadotropin, Blastula, Pregnancy outcome