Abstract: Although great progress has been made in assisted reproductive technology (ART) since the mid-1990s, the embryo implantation rate after transfer is relatively low. Embryo implantation is a complex process involving the interaction between the embryo and the endometrium. Among the many factors involved in implantation, human chorionic gonadotropin (hCG) plays a key role. As one of the early embryonic signals secreted by embryos before implantation, hCG mRNA began to transcribe as early as the embryonic 8-cell stage, while blastocysts began to express hCG before implantation. Studies have shown that hCG, as an important medium in the early stage of embryo implantation, promotes the endometrial decidualization, angiogenesis, trophoblast invasion and maternal immune tolerance by improving endometrial receptivity, which is beneficial to successful embryo implantation. In this paper, we summarize the application of human chorionic gonadotropin in embryo transfer and its research progress.

Key words: Chorionic gonadotropin, Reproductive techniques, assisted;, Embryo transfer, Intrauterine injection;, Receptivity of endometrium