Even though most of the obstetrical and perinatal results were alike amongst women on metformin and insulin, but this randomized prospective trial found metformin to be effective in terms of improved postprandial glycemic control, reduced incidences of low blood sugar, low maternal weight gain, and a low failure rate.

To compare the effectiveness of metformin and insulin in terms of glycemic control, obstetrical and perinatal outcomes in cases of gestational diabetes mellitus (GDM) not appropriately controlled with lifestyle modifications.

Two hundred women with GDM aged 18-45 years, in the second or third trimesters were randomized to receive metformin (metformin-treated group) or insulin (insulin-treated group) with 100 patients in each. The main outcomes were:

• Glycemic control: Mean blood glucose, pre-prandial and postprandial and hypoglycemic episodes
• Obstetrical and perinatal results and problems: Type of labor, prematurity, fetal macrosomia, large for gestational age, admissions to neonatal care unit, hypertensive diseases, respiratory distress syndrome, low blood sugar, jaundice

Patients in the metformin group had significantly better postprandial glycemia following lunch and/or dinner than insulin. Hypoglycemic episodes were considerably more common in the insulin-treated group (55.9%) than metformin (17.7%). Women on metformin treatment gained less weight from the study registration to the prepartum visit (36 to 37 gestational weeks). Also, these women had significantly lesser labor inductions and cesarean deliveries. Lower cesarean delivery rate for women on metformin was not linked with large or small for gestational age or macrosomia, or other pregnancy associated complications.

As compared to insulin, metformin leads to better postprandial glycemic control for some meals alongwith a lower risk of hypoglycemic episodes, less maternal weight gain, and low failure rate when used alone.