Metformin's effect on first-year weight gain: a follow-up study.

BACKGROUND The impact of metformin medication in pregnant women with polycystic ovary syndrome on weight gain during pregnancy and after delivery and the impact on growth of the offspring are essentially unexplored. METHODS This is a follow-up study of a randomized controlled trial (The Metformin treatment in pregnant PCOS women study), conducted in 11 secondary care centers. Women with PCOS were randomized to metformin (2000 mg daily) or placebo from first trimester to delivery. Questionnaires were sent to 256 participants 1 year postpartum. Maternal weight development in pregnancy and the first year after delivery and offspring anthropometry at birth and weight 1 year postpartum were registered. RESULTS Women randomized to metformin gained less weight during pregnancy compared with those in the placebo group. In the newborns, there was no difference between the 2 groups in weight or length. One year postpartum, women who used metformin in pregnancy lost less weight and their infants were heavier than those in the placebo group (10.2 ± 1.2 kg vs 9.7 ± 1.1 kg, P = .003). CONCLUSIONS Women randomized to metformin were heavier in the first trimester, gained less weight in pregnancy, and lost less weight in the first year postpartum compared with women randomized to placebo. Children exposed to metformin weighed more at 1 year of age.