Abstract: Objective: To compare the pregnancy outcomes of spontaneous natural cycle versus human chorionic gonadotropin（hCG） and gonadotropic releasing hormone agonist （GnRHa） induced cycle in those women with frozen-thawed embryo transfer. Methods：The 273 natural cycles of the frozen-thawed embryo transfer were retrospectively analyzed in our reproductive center from October，2011 to October，2013. Those cycles were divided into three groups according to ovulation inducing methods：group A，spontaneous ovulation（n=181）；group B，triggering with hCG（n=47）；group C，triggering with GnRHa（n=45）. The pregnancy outcome and other clinical parameters were compared among three groups. Results：①There were not significantly differences in age, endometrial thickness on the day of transfer, embryonic number of transfer and the rate of high-quality embryo among three groups（P＞0.05）. ②The clinical pregnancy rate in group A（56.4%） was significantly higher than that in group C（33.3%，P＜0.01），while there was not significantly difference in this rate between group A and group B（P＞0.016 7）. Conclusions：The adverse effect of hCG induced ovulation on the pregnancy outcome was not significant in the frozen-thawed embryo transfer, while GnRHa induced ovulation may affect the pregnancy outcome of the frozen-thawed embryo transfer.

Key words: Embryo transfer, Fertilization in vitro, Ovulation induction, Pregnancy outcome