Metformin exposure in infants of mothers with type 2 diabetes did not affect growth at 2 years.

Insulin is the preferred agent for managing type 2 diabetes during pregnancy, because the safety profile of metformin, which crosses the placenta, is unclear. Uncertainty about long-term effects of in utero metformin exposure on childhood growth limits its use in pregnant women; in fact, research has suggested that such exposure might promote childhood obesity. In a previously published study of neonatal outcomes, researchers randomised pregnant women with type 2 diabetes to insulin alone or insulin plus metformin (Lancet Diabetes Endocrinol 2020; 8: 834-844). Now, researchers have evaluated postnatal growth during follow up of 283 infants from this study.

At 2 years of age, children who had been exposed to metformin and unexposed children had no significant difference in body mass index (BMI) or skinfold thickness. Although the mean BMI of infants in this study was not in the overweight or obese range, it was one standard deviation above the WHO population reference mean. Higher maternal BMI, lower socioeconomic status, shorter breastfeeding duration and shorter childhood sleep duration – but not metformin exposure – were all associated with higher BMI at 24 months. 

Comment: Although insulin remains the preferred agent for treating type 2 diabetes during pregnancy, this study provides reassurance for using metformin as a necessary adjunct or alternative. Infants of mothers with type 2 diabetes are at excess risk for adverse cardiometabolic outcomes later in life, so promoting longer breastfeeding duration and longer childhood sleep duration (admittedly not an easy task) might be one strategy for optimising the care of infants whose mothers have diabetes.

Marie Claire O’Dwyer, MB BCh BAO, MPH, Clinical Assistant Professor in Family Medicine, University of Michigan Medical School, Ann Arbor, USA.

Feig DS, et al. Outcomes in children of women with type 2 diabetes exposed to metformin versus placebo during pregnancy (MiTy Kids): a 24-month follow-up of the MiTy randomised controlled trial. Lancet Diabetes Endocrinol 2023; 11: 191-202.

This summary is taken from the following Journal Watch titles: General Medicine, Ambulatory Medicine, Women’s Health, Pediatrics and Adolescent Medicine.