How does metformin compare to insulin for diabetes during pregnancy?

This study compared metformin (Glucophage) to insulin for women with diabetes during pregnancy. It found that metformin was equally good at preventing high blood sugar, but led to less hypoglycemia (dangerously low blood glucose), less weight gain, and fewer cesarean sections.

Gestational diabetes (GD) is one of the most common health conditions a woman can develop during pregnancy. GD involves high levels of glucose (sugar) in the blood. GD increases the risks of pregnancy for both the mother and baby and women with GD are also more likely to develop type 2 diabetes later in life.

For women with GD whose blood glucose is not well controlled through dietary changes, there are several options. Synthetic insulin is effective at controlling blood sugar, and it cannot pass through the placenta to the baby. However, insulin can cause hypoglycemia if the dose is not exactly right. Using insulin also requires taking multiple injections daily, and can increase weight gain during pregnancy.

Metformin is a common diabetes medication taken as a pill. Metformin is sometimes used during pregnancy. Metformin can cross the placenta and reach the baby, but it does not cause birth defects. However, some doctors are reluctant to use metformin during pregnancy for this reason.

It is not clear how pregnancy outcomes compare for women using metformin versus insulin.

This study included 200 women with GD in their second or third trimester of pregnancy. 100 women were randomly assigned to take metformin, and the other 100 took insulin. Either long-lasting daily insulin (Detemir) or short-acting mealtime insulin (Aspart) or both were used as needed. All of the women were also given diet and exercise advice. The two groups were followed throughout pregnancy and childbirth. However, 21.3% of the metformin group later needed to take insulin as well, due to their high blood glucose levels.

The two groups had similar glucose levels both fasting and after eating. This was true two weeks after starting treatment, and also shortly before their due date. They also had similar glycated hemoglobin (HbA1c), which is a measure of blood glucose control over the previous 2-3 months.

Significantly fewer women using metformin had an episode of hypoglycemia compared to those using insulin (17.7% vs. 55.9%). Women using metformin also had less weight gain (1.35 vs. 3.87 kg; 3.0 vs. 8.5 lbs). The two groups had similar rates of high blood pressure or preeclampsia.

Women using metformin had labor artificially induced less often (45.7% vs. 62.5%). Metformin also led to fewer Cesarean section births (27.6% vs. 52.6%).

This study found that metformin treated high blood glucose equally as well as insulin in women with GD, but led to less hypoglycemia and fewer childbirth interventions.

Insulin is typically used by people with worse diabetes. Because of this, the patients’ obstetricians, who were not involved in the study, may have used more childbirth interventions.