Abstract: Objective: To assess the effect of female overweight and obesity on the clinical outcomes of in vitro fertilization-embryo transferation (IVF-ET). Methods：This is a retrospective study of 516 women aged ＜38 years undergoing nondonor IVF cycles in a university affiliated hospital. They were classified into two groups: the normal weight group（Group A: BMI 18.5～24.9 kg/m2, n=467） and the overweight and obese group （Group B: BMI≥25 kg/m2, n=49）. Clinical treatment and outcomes（fertilization, implantation, pregnancy, miscarriage and live birth rate） were compared. Results：The total dose of gonadotrophin（Gn） and stimulation days in group B were significantly larger than those in group A（P＜0.05）, while the E2 level on the day of hCG administration in group B was significantly lower（P＜0.05）. There were not significant differences in the number of harvested oocytes, the implantation rate, the clinical pregnancy rate and the live birth rate between two groups（P＞0.05）. Interestingly, the fertilization rate in group A was significantly higher than that in group B（χ2=8.102，P=0.004）. Conclusions：Female overweight and obesity results in the prolonged Gn stimulation, the increased dose of Gn and the lowered fertilization rate, which had negative effect on IVF outcomes.

Key words: Body weight, Overweight, Obesity, Fertilization in vitro, Embryo transfer