Fourteen RCTs (2,240 participants, range 31 to 626) were included in the review. Five RCTs were reported to be double blind. There was no blinding in five RCTs.
Compared with clomiphene citrate, metformin alone was associated with a significant reduction in the rate of live birth (OR 0.48, 95% CI 0.31 to 0.73; four RCTs; Ι²=77%) and a significant reduction in the rate of ovulation (OR 0.48, 95% CI 0.41 to 0.57; two RCTs; Ι²=89%). Significant heterogeneity was found in both outcomes. There was no significant difference in the rate of pregnancy between the two groups.
Compared with clomiphene citrate alone, metformin plus clomiphene citrate was associated with a significant increase in the rate of ovulation (OR 1.6, 95% CI 1.2 to 2.1; eight RCTs). There were no significant differences in the rates of live birth (four RCTs) and pregnancy (10 RCTs) between the two groups. Significant heterogeneity was found in the outcomes of ovulation (Ι²=63.1%) and and pregnancy (Ι²=77.4%).
Subgroup analyses were reported.