Abstract: Objective： To investigate the effects of hCG at different dosages on embryo quality and IVF-ET outcomes，so as to discuss the feasibility and safety of the lowered dosage of hCG in inducing ovulation to prevent OHSS. Methods：327 patients who had high risks of OHSS were divided into two groups as follows，group A：204 patients with hCG dosage of 2 000-4 000 IU；group B：123 patients with hCG dosage of 10 000 IU. Age，initial Gn dosage，total dosage of Gn，No. of egg retrieval，clinical pregnancy rate and the OHSS rate，were compared between two groups. Results：There were no significant differences in age，BMI，initial and total dosage of Gn，days for COH between group A and B. The differences of the E2 levels on hCG injection day，No. of growth follicles，No. of egg retrieval，fertilization rates，2PN embryos，gradeⅠembryos，No. of ET and frozen embryo between two groups were statistically insignificant. The rate of severe OHSS in group A was lower than that in group B. The clinical pregnancy rate per egg retrieval cycle in group A was significantly lower than that in group B，while the differences of the pregnancy rates per transfer cycle between two groups were statistically insignificant. Ｃｏｎｃｌｕｓｉｏｎs： The decreasing dosage of hCG for ovulation induction in high risk OHSS patients during IVF-ET has no negative influence for egg maturation，insermination and embryo quality，but can effectively prevent the severe OHSS.

Key words: Fertilization in vitro, Embryo transfer, Ovarian hyperstimulation syndrome, Ovulation induction, Chorionic gonadotropin, Ovum