Obesity in pregnancy is linked with a greater risk of adverse short-term and long-term outcomes in the mother as well as the baby. Efforts to reduce pregnancy complications have focused mainly on lifestyle interventions. However, they have not shown favorable results. An alternative approach is the use of metformin, an oral hypoglycemic agent that reduces insulin resistance. It is widely used for treating gestational diabetes mellitus, with no associated congenital anomalies. Hyperglycemia and increased insulin resistance often occur with obesity and may underline the link between obesity and fetal macrosomia, as well as other pregnancy complications. Metformin helps by ameliorating insulin sensitivity, and in pregnant women with gestational diabetes, it causes less weight gain than that occurs in people who do not take metformin.

In a double-blind, placebo-controlled trial, pregnant women without diabetes who had a body-mass index (BMI) > 35 were randomly allocated to receive either metformin or placebo from 12-18 weeks of gestation until delivery. There were 202 women in the metformin group and 198 in the placebo group. No significant between-group difference in the median neonatal birth-weight z score was reported. The median maternal gestational weight gain was comparatively lower in the metformin group than in the placebo group (4.6 kg [interquartile range, 1.3 to 7.2] vs. 6.3 kg [interquartile range, 2.9 to 9.2], P < 0.001). In addition, the incidence of preeclampsia was lower in the metformin group (3.0% vs. 11.3%; odds ratio, 0.24; 95% confidence interval, 0.10 to 0.61; P=0.001). Thus, it was suggested that among women without diabetes who had a BMI > 35, antenatal metformin therapy reduced maternal weight gain but not neonatal birth weight.

Reference

1. SyngelakiA, Nicolaides KH, Balani J, et al. Metformin versus Placebo in Obese Pregnant Women without Diabetes Mellitus. N Engl J Med. 2016 Feb 4;374(5):434-43.