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Randomized Controlled Trial Suggests Metformin Offers Benefits During Pregnancy
Researchers randomly assigned 502 pregnant women with type 2 diabetes who were using insulin to add metformin (1,000 milligrams twice daily) or a placebo to their treatment regimen. As women neared the end of pregnancy, at 34 weeks’ gestation, the participants on metformin had lower average fasting blood sugar levels than their counterparts who didn’t take metformin (41.0 versus 43.2 millimoles per mol) and used less insulin (1.1 units versus 1.5 units per kilogram [kg] per day). With metformin, women also gained less weight than participants on placebo (7.2 versus 9.0 kg), and were also 15 percent less likely to require a cesarean delivery and 42 percent less likely to have a baby that was large for its gestational age, in the 97th percentile for birth weight. As mentioned, though, there was one potential downside. Women taking metformin were also about twice as likely to have babies that were small for their gestational age, an outcome that happened to 13 percent of women on metformin compared with 7 percent on placebo. “All women with type 2 diabetes in pregnancy using insulin should consider taking metformin,” says the lead study author, Denice Feig, MD, a professor of medicine at the University of Toronto. Again, this is a treatment choice that a woman needs to make with her doctor on the basis of her individual health and pregnancy. RELATED: How to Treat Diabetes From the Inside Out
Risk of Small-for-Gestational-Age Babies
But women shouldn’t take metformin while pregnant if they had a prior pregnancy with a baby who was small for its gestational age, Dr. Feig adds. And if women taking metformin have a baby who appears small for its gestational age during a prenatal checkup, they should consider stopping metformin, Feig advises. Because the study focused on women with type 2 diabetes who were taking insulin to manage their blood sugar, it’s not clear how metformin would impact pregnancy outcomes for mothers with diabetes who are not taking insulin during pregnancy. It’s also not clear whether the results would apply to women who have gestational diabetes, a type of the disease that develops for the first time during pregnancy. People with type 2 diabetes can’t use the hormone insulin effectively to regulate the amount of sugar in the blood. Metformin works by increasing the body’s response to insulin and by reducing the amount of sugar absorbed from food.
Metformin Safety in Pregnancy Still an Open Question
The American Diabetes Association (ADA) recommends metformin only for pregnant women with type 2 diabetes who don’t achieve good blood sugar control with insulin, because metformin can cross the placenta to reach developing babies, according to guidelines published in the January 2021 issue of Diabetes Care. The exact health impact of metformin exposure in the womb isn’t well understood, according to an analysis published October 2017 by the Cochrane Database of Systematic Reviews. This analysis found that the risk of babies being large for their gestational age was similar with metformin and insulin, and the risk of cesarean section deliveries was lower with metformin. But the researchers described this evidence as “low quality” and noted that more research is needed to determine long-term health for babies exposed to metformin during pregnancy. If it’s not well managed, diabetes during pregnancy can increase the risk of birth defects, stillbirth, and preterm birth, according to the CDC. For this reason, the CDC recommends that women with type 2 diabetes try to maintain healthy blood sugar levels prior to conception. Once they become pregnant, the CDC advises women to follow a healthy eating plan, get plenty of exercise, and use insulin as needed to manage their blood sugar. “Poorly controlled diabetes with high blood sugar is more dangerous than the drugs used to treat diabetes,” says Adrian Teo, PhD, an assistant professor at the National University of Singapore who wasn’t involved in the current study. For some pregnant women who don’t achieve good blood sugar control with insulin alone, adding metformin to their treatment regimen may help reduce the risk of outcomes like miscarriage and stillbirth, Dr. Teo says. “Metformin can help regulate blood glucose levels in the mothers,” Teo says. “However, the long-term impact of metformin on the development of the babies remains to be studied in greater detail with longer-term follow-ups.”
