Early Metformin in Gestational Diabetes A Randomized Clinical Trial

Importance Gestational diabetes is a common complication of pregnancy and the optimal management is uncertain.Objective To test whether early initiation of metformin reduces insulin initiation or improves fasting hyperglycemia at gestation weeks 32 or 38.Design, Setting, and Participants Double-blind, placebo-controlled trial conducted in 2 centers in Ireland (one tertiary hospital and one smaller regional hospital). Participants were enrolled from June 2017 through September 2022 and followed up until 12 weeks' postpartum. Participants comprised 510 individuals (535 pregnancies) diagnosed with gestational diabetes based on World Health Organization 2013 criteria.Interventions Randomized 1:1 to either placebo or metformin (maximum dose, 2500 mg) in addition to usual care.Main Outcomes And Measures The primary outcome was a composite of insulin initiation or a fasting glucose level of 5.1 mmol/L or greater at gestation weeks 32 or 38.Results Among 510 participants (mean age, 34.3 years), 535 pregnancies were randomized. The primary composite outcome was not significantly different between groups and occurred in 150 pregnancies (56.8%) in the metformin group and 167 pregnancies (63.7%) in the placebo group (between-group difference, -6.9% [95% CI, -15.1% to 1.4%]; relative risk, 0.89 [95% CI, 0.78-1.02]; P = .13). Of 6 prespecified secondary maternal outcomes, 3 favored the metformin group, including time to insulin initiation, self-reported capillary glycemic control, and gestational weight gain. Secondary neonatal outcomes differed by group, with smaller neonates (lower mean birth weights, a lower proportion weighing >4 kg, a lower proportion in the >90% percentile, and smaller crown-heel length) in the metformin group without differences in neonatal intensive care needs, respiratory distress requiring respiratory support, jaundice requiring phototherapy, major congenital anomalies, neonatal hypoglycemia, or proportion with 5-minute Apgar scores less than 7.Conclusion and relevance Early treatment with metformin was not superior to placebo for the composite primary outcome. Prespecified secondary outcome data support further investigation of metformin in larger clinical trials.