Abstract: Objective：To evaluate of the effectiveness of treatment with metformin in PCOS patients undergoing IVF. Methods：CBM disc，Wan Fang，CNKI，VIP，PubMed，PML，FMJS，Duxiu scholar search （www.duxiu.com） and 9 related journals were searched for the randomized controlled trails （RCTs） on the metformin treatment in PCOS patients undergoing IVF. The search time was from the first published to the end of December，2011. Meta-analysis was performed after quality assessment. Results：Six published studies with 607 patients were included. Meta-analysis showed that E2 value on the hCG day，OHSS rate，and cancellation rate of the metformin group were significantly lower than those of the control group，whereas pregnancy rate of the metformin group was significantly higher （P＜0.05）. No significant differences were found in the stimulation period （days），total amount of gonadotropin, number of oocytes retrieved，miscarrage rate，and live birth rate between the metformin group and the placebo group. Conclusions：Treatment with metformin can significantly increase pregnancy rate，and reduce risk of OHSS，in PCOS patients undergoing IVF.

Key words: Metformin, Polycystic ovary syndrome, Fertilization in vitro, Meta-analysis, Systematic review