Abstract: Objective To investigate the effect of the duration of gonadotropin(Gn)in the controlled ovarian hyper stimulation(COH)cycle on the number of eggs obtained, embryo development, and pregnancy outcome in those with good ovarian response, and to analyze the possible factors that contributed to the prolongation of Gn use. Methods A total of 3 054 patients undergoing in vitro fertilization-embryo transfer(IVF-ET)were divided into groups A, B, and C according to the days of Gn use(group A: Gn days≤7 d; group B: 8 d ≤Gn days ≤11 d; group C: Gn days ≥12 d).The baseline data, COH and pregnancy outcomes were compared. The possible factors leading to the prolongation of Gn use were analyzed with Logistics regression. Results The highest BMI and FSH levels were found in group C(P=0.001), while the lowest AMH and AFC levels were found in group C(P=0.022, 0.002). The Gn starting dose, total Gn dose and downregulation days in group A were the least among the three groups(P<0.001). There were no significant differences among the three groups in indicators related to COH treatment and pregnancy outcomes(P=0.86, 0.57, 0.91, 0.64). Logistics regression showed that higher BMI and Gn starting dose were risk factors of prolonged Gn use, while higher AMH and AFC, lower FSH level and shorter downregulation days were protective factors of prolonged Gn use. Conclusion The duration of Gn use has no significant effect on the pregnancy outcomes of IVF-ET. Higher BMI and Gn starting dose can significantly prolong Gn use, while higher AMH and AFC, lower FSH level and shorter downregulation days can significantly shorten Gn use.

Key words: Long GnRHa protocol, Usage days of gonadotropin, In vitro fertilization and embryo transfer(IVF-ET), Pregnancy outcome