Does metformin use in pregnancy lead to childhood weight gain?

This study looked at the use of metformin (Glucophage) for the management of type 2 diabetes (T2D) in pregnancy. The study showed that compared to infants exposed to placebo, those exposed to metformin during pregnancy did not show any signs of increased weight or body mass index (BMI; a measurement of weight in relation to height) after two years.

T2D is a very common condition that can be difficult to manage during pregnancy. Metformin is increasingly used to help manage blood sugars in pregnant women with T2D. However, there are concerns that by lowering blood glucose, metformin may cause inadequate nutrition for the baby. This can trigger changes in the baby's body that will make them more prone to weight gain and obesity in the future. However, because the babies of women with T2D are usually over-nourished, it is possible that metformin simply maintains a normal level of nutrition for them, without any ill effects. It is important to evaluate whether metformin use during pregnancy has effects on the future weight of the babies. 

This study involved 226 infants, belonging to mothers with T2D. 111 infants had been exposed to metformin during pregnancy (1g twice daily). 115 infants had been exposed to a placebo. Infants were measured at 3, 6, 12, 18, and 24 months. Measurements were taken of their skin folds to estimate their body fat, as well as their BMI.

At 2 years of age, there was no significant difference in measurements between infants exposed to metformin in pregnancy and those exposed to placebo. 

Male infants exposed to metformin gained weight more quickly during the initial months. However, by 24 months they measured the same as those infants who had not been exposed to metformin.

This study showed that infants of mothers with T2D exposed to metformin during pregnancy were not at increased risk of weight gain within the first two years of life, compared to infants exposed to placebo.

This study only followed infants for 2 years. It is possible that excess weight gain does not occur until later in childhood. Further studies with longer follow up are required to see if metformin causes any effects in later childhood.