Metformin in gestational diabetes mellitus: A double‐blind placebo‐controlled randomized trial

OBJECTIVE: To evaluate the impact of preemptive metformin on the level of glycosylated hemoglobin (HbA1c) at 36 weeks of pregnancy in women with gestational diabetes mellitus controlled by diet change (GDMA1). METHODS: A randomized, double-blind, placebo-controlled trial was performed in a university hospital. Women with GDMA1 were recruited at 16-30 weeks of pregnancy and randomized to oral metformin 500 mg twice daily or identical placebo tablets to delivery. Level of HbA1c was taken at recruitment and at 36 weeks of pregnancy. The primary outcome was the change in level of HbA1c at recruitment and 36 weeks of pregnancy. RESULTS: Data from 106 participants were analyzed. The level of HbA1c during pregnancy increased significantly with a mean increase of 0.20% ± 0.31% (P < 0.001; metformin) versus 0.27% ± 0.31% (P < 0.001; placebo). An increment of 0.07% across trial arms was not significant (P = 0.310). Mean birth weight was significantly lower in the metformin group (2.81 ± 0.41 kg vs 2.98 ± 0.37 kg; P = 0.030). Rates of macrosomia (≥3.5 kg; 0/53 [0%] vs 4/53 [8%]; P = 0.123) and low birth weight (<2.5 kg; 11/53 [21%] vs 5/53 [9%]; P = 0.102) were not significantly different. CONCLUSION: Preemptive metformin did not prevent the level of HbA1c at 36 weeks of pregnancy from rising nor significantly reduce the increase of HbA1c. Mean birth weight was significantly lower in the metformin arm with a non-significant trend to low birth weight, which is concerning. ISRCTN: ISRCTN10845466.