Metformin should be considered in the treatment of gestational diabetes: a prospective randomised study

Objective: To examine if oral metformin is as effective as insulin in the prevention of fetal macrosomy in pregnancies complicated with gestational diabetes mellitus (GDM).

Design: Open-label prospective randomised controlled study.

Setting: Maternity outpatient clinics in a secondary and tertiary level hospital in Finland.

Sample: One hundred women with GDM who did not attain euglycaemia with diet.

Methods: Women were randomised to therapy with insulin (n = 50) or oral metformin (n = 50).

Main outcome measures: Incidence of large-for-gestational-age (LGA) infants and neonatal morbidity.

Results: There were no statistically significant differences in the incidence of LGA (8.5 versus 10.0%, P = 0.97), mean birthweight, mean cord artery pH or neonatal morbidity between the insulin and metformin groups. Fifteen (31.9%) of the 47 women randomised to metformin needed supplemental insulin. They were more obese (with a body mass index of 36 versus 30 kg/m(2), P = 0.002), had higher fasting blood glucose levels in an oral glucose tolerance test (6.1 versus 5.0 mmol/l, P = 0.001) and needed medical treatment for GDM earlier (26 versus 31 gestational weeks, P = 0.002) than women who were normoglycemic with metformin. There was a tendency to a higher rate of caesarean sections in the metformin group than in the insulin group (RR 1.9; 95% CI 0.99-3.71).

Conclusions: Metformin seems to be suitable for the prevention of fetal macrosomy, especially in lean or moderately overweight women developing GDM in late gestation. Women with considerable obesity, high fasting blood glucose and an early need for pharmacological treatment may be more suitable for insulin therapy.