Effect comparison of metformin with insulin treatment for gestational diabetes: a meta-analysis based on RCTs

Purpose To compare the effects of metformin with insulin on maternal and neonatal outcomes in gestational diabetes mellitus (GDM). Methods A literature search in PUBMED, EMBASE, Science Direct, Springer link, and Cochrane library was conducted using the following search terms: "Gestational Diabetes'' or "GDM'', and "insulin'' and "metformin''. Quality assessment of included studies was determined with Quality Assessment of Diagnostic Accuracy Studies. Review Manger 5.2 was used to analyze mean difference (MD)/risk ratio (RR) and 95 % confidence interval (CI) in random-effects model or fixed-effects model depending on the level of heterogeneity. Results A total of 11 studies were identified. There was no significant difference of the effect on maternal outcomes between the two treatments in glycohemoglobin A1c levels (P = 0.37), fasting blood glucose (P = 0.66), and the incidence of preeclampsia (P = 0.26); whereas, significantly reduced results were found in the metformin group in pregnancy-induced hypertension (PIH) rate (RR = 0.53, 95 % CI 0.31-0.90, P = 0.02), average weight gains after enrollment (MD = -1.28, 95 % CI -1.54 to -1.01, P < 0.0001), and average gestational ages at delivery (MD = 0.94, 95 % CI -0.21 to -0.01, P = 0.03). Regarding neonatal outcomes, when compared with insulin group, metformin presented significantly lower average birth weights (MD = -44.35, 95 % CI -85.79 to -2.90, P = 0.04), incidence of hypoglycemia (RR = 0.69, 95 % CI 0.55-0.87, P = 0.001) and neonatal intensive care unit (NICU) (RR = 0.82, 95 % CI 0.67-0.99, P = 0.04). Conclusion Metformin can significantly reduce several adverse maternal and neonatal outcomes including PIH rate, incidence of hypoglycemia and NICU, thus it may be an effective and safe alternative or additional treatment to insulin for GDM women.