Abstract: Objective：To compare the pregnancy outcomes of artificial insemination in natural cycle and ovulation cycle for women with different body mass index. Methods：This retrospective study included 1 707 female patients undergoing artificial insemination by donor from March 2011 to April 2017. There were 1 314 cases in normal weight group （Among them，there were 1 162 natural cycle and 152 artificial cycles, 18.5 kg/ m2≤BMI＜24 kg/m2），320 cases in excess weight group（Among them，there were 270 natural cycle and 50 artificial cycles, 24 kg/m2≤BMI＜28 kg/m2） and 73 cases in obesity group（Among them，there were 54 natural cycle and 19 artificial cycles, BMI≥28 kg/m2）. The biochemical pregnancy rate，clinical pregnancy rate，abortion rate and live birth rate of AID were compared in women with different body mass index, and between two different cycles. Results：In normal weight group, the abortion rate of AID in artificial cycles was significantly higher than that in natural cycles（29.03%，9/31 vs. 11.45%，30/262，χ2=0.589，P=0.014），however there were significant differences in the biochemical pregnancy rate, clinical pregnancy rate and live birth rate when compared between two different cycles (all P＞0.05). In excess weight group, the clinical pregnancy rate and live birth rate in natural cycles（23.33%，63/270：21.48%，58/270）were significantly higher than those in artificial cycles（10%，5/50：8%，4/50，χ2=4.482，P=0.034；χ2=4.908，P=0.027），however there were no significant differences in the biochemical pregnancy rate and the abortion rate when compared between two different cycles（both P＞0.05），so as. However，in obesity group，the difference of pregnancy outcomes was no significant when compared between natural cycles and ovulation cycles （P＞0.05）. Conclusions：Some parameters of clinical outcomes of natural cycles may be better than those of ovulatory cycles in those women undergoing AID treatment. Especially, the pregnancy outcome of natural cycles is better than that of ovulatory cycles in those women with excess weight. The natural cycle should be advocated for those suitable women.

Key words: Insemination, artificial, Embryo transfer, Body mass index, Pregnancy outcome