Effectiveness of Metformin in the Prevention of Gestational Diabetes Mellitus in Obese Pregnant Women

Objective To assess the effectiveness of metformin in the incidence of gestational diabetes mellitus (GDM) in obese pregnant women attending a public maternity hospital in Joinville, Santa Catarina, Brazil. Methods Randomized clinical trial including obese pregnant women with a body mass index (BMI) ≥ 30 kg/m(2), divided into two groups (control and metformin). Both groups received guidance regarding diet and physical exercise. The participants were assessed at two moments, the first at enrollment (gestational age ≤ 20) and the second at gestational weeks 24–28. The outcomes assessed were BMI and gestational diabetes mellitus (GDM) diagnosis. The data distribution was assessed with the Friedman test. For all the analytical models, the p-values were considered significant when lower than 0.05. The absolute risk reduction was also estimated. Results Overall, 164 pregnant women were assessed and further divided into 82 participants per group. No significant difference was observed in BMI variation between the control and metformin groups (0.9 ± 1.2 versus 1.0 ± 0.9, respectively, p = 0.63). Gestational diabetes mellitus was diagnosed in 15.9% (n = 13) of the patients allocated to the metformin group and 19.5% (n = 16) of those in the control group (p = 0.683). The absolute risk reduction was 3.6 (95% confidence interval 8.0–15.32) in the group treated with metformin, which was not significant. Conclusion Metformin was not effective in reducing BMI and preventing GDM in obese pregnant women.