Effect sizes were similar across all diabetes in pregnancy groups: insulin (15 studies28,31,32,41–47,50–54, n = 3519) (Fig. 4b), glyburide (3 studies33,35,49, n = 463) (Fig. 4c) and placebo (OR 1.35, 95% CI 0.87–2.09; I2 = 0%, p = 0.18) (1 study36, n = 461). This evidence concerns the gene INS and diabetes mellitus.