Postnatal effects of metformin on growth in children of mothers with gestational diabetes mellitus

Gestational diabetes mellitus (GDM) has an incidence of 7.6%. Insulin is the standard treatment but metformin, which crosses the placental barrier, has become an easy-to-administer alternative, although its long-term effects remain uncertain. Objective: To evaluate weight and height development up to 6 years of age of children born to mothers with GDM treated with metformin and compare them with those treated with insulin. Patients and Method: A retrospective cohort study was conducted at the Hospital Italiano de Buenos Aires (2015-2018), including children born to mothers with GDM treated with metformin or insulin. Newborns of mothers without pharmacological treatment were excluded. Maternal characteristics such as age, body mass index (BMI) at the beginning of pregnancy, weight gain, first pregnancy, pregnancy outcome, and treatment were evaluated, as well as the newborn characteristics such as large for gestational age (LGA), small for gestational age (SGA), and preterm. Weight and height development controls were conducted at 6, 12, 24, 48, and 72 months, standardized in Z-scores. Inverse Probability of Treatment Weighting (IPTW) and Generalized Estimating Equations (GEE) were used. Results: A total of 187 newborns were included, with IPTW showing good covariate balance between groups. No significant differences were observed in the Z-scores of BMI, weight, and height between the groups. Conclusions: Both insulin and metformin have similar effects on the weight and height development of children during the first 6 years from birth, born to mothers with GDM. Further research is needed to confirm these results.