Metformin as a Safe Option to Insulin in Gestational Diabetes Mellitus: a Retrospective Study

When pharmacological treatment is needed to reach control of gestational diabetes mellitus (GDM), insulin is still first-line agent but metformin has been progressively pointed as an effective alternative. Our aim is to confirm whether metformin is an effective and safe option to insulin, by comparing maternal and foetal outcomes between women with GDM treated with these drugs. Retrospective study including 399 women with GDM, 135 needing pharmacological treatment. Comparison of demographic features, risk factors for GDM, maternal and foetal outcomes between women treated with insulin (G1, 41/135) and those treated with metformin (G2, 94/135). X2/Fisher tests were performed. Significance was set at p < 0.05. Both groups showed similar features and risk factors for GDM, except for chronic hypertension, more prevalent in G1. Therapy with insulin showed poorer metabolic control with higher rate of pregnant with HbA1c ≥ 6% (42 mmol/mol) (25.6 vs 4.5%, p = 0.001) and more polihydramnios (14.6% vs 3.2%, p = 0.023). A higher rate of caesarean was observed in G1, however, with no statistical difference (42.5% vs 26.9%, p = 0.076). There were more newborns weighing < 2500 g in women treated with metformin. No other outcome showed difference with statistical significance, namely maternal weight gain, macrosomia or neonatal comorbidities. Metformin allowed a good metabolic control with maternal and foetal outcomes similar to insulin. Metformin has proven effective as a pharmacological option to insulin. Prospective and randomized studies are needed as well as evaluation of long term benefits of metformin.