Pregnancy outcomes in women with gestational diabetes treated with metformin or insulin: a case-control study

Aims To compare maternal and neonatal outcomes in women with gestational diabetes mellitus (GDM) treated with either metformin or insulin. Methods One hundred and twenty-seven women with GDM not adequately controlled by dietary measures received metformin 500 mg twice daily initially. The dose was titrated to achieve target blood glucose values. Pregnancy outcomes in the 100 women who remained exclusively on metformin were compared with 100 women with GDM treated with insulin matched for age, weight and ethnicity. Results There were no significant differences in baseline maternal risk factors. Women treated with insulin had significantly greater mean (sem) weight gain from enrolment to term (2.72 +/- 0.4 vs. 0.94 +/- 0.3 kg; P < 0.001). There was no difference between the metformin and insulin groups, respectively, comparing gestational hypertension (6 vs. 7%, P = 0.9), pre-eclampsia (9 vs. 2%, P = 0.06) induction of labour (26 vs. 24%, P = 0.87) or rate of Caesarean section (48 vs. 52%, P = 0.67). No perinatal loss occurred in either group. Neonatal morbidity was improved in the metformin group; prematurity (0 vs. 10%, P < 0.01), neonatal jaundice (8 vs. 30%, P < 0.01) and admission to neonatal unit (6 vs. 19%, P < 0.01). The incidence of macrosomia (birthweight centile > 90) was not significantly different [metformin (14%) vs. insulin (25%); P = 0.07]. Conclusions Women with GDM treated with metformin and with similar baseline risk factors for adverse pregnancy outcomes had less weight gain and improved neonatal outcomes compared with those treated with insulin.