Metformin, a widely used diabetes medication often prescribed to pregnant women to manage blood sugar and prevent complications, may carry long-term risks for the unborn child, a recent study revealed.

Researchers discovered that the drug crosses the placenta, potentially resulting in fetal growth restrictions and increasing the risk of obesity and insulin resistance in childhood.

"We know that when a pregnant woman is obese and has a condition like diabetes, her child is much more likely to develop obesity and diabetes. Because of the widespread use of metformin in pregnant mothers, it is important for us to understand whether the drug is beneficial to babies over the long term, or whether it has unintended consequences," said study co-author Jed Friedman in a news release.

The study results published in the American Journal of Obstetrics and Gynecology suggest that metformin freely crosses the placenta and accumulates in the fetal kidneys, liver, intestines, placenta, amniotic fluid, and urine. Researchers found that the drug's levels in fetal urine are almost as high as those in the mother's.

"That accumulation during pregnancy was associated with growth restriction in the kidneys, liver, skeletal muscle, heart, and fat deposits that support the abdominal organs, all of which served to lower the fetus's body weight," the news release stated.

Another striking finding was that the level of metformin in the child's system did not differ according to the mother's diet.

"Many drugs undergo 'first-pass' metabolism by becoming absorbed first in the liver, which decreases the concentration before it continues through the body. However, metformin does not experience the first-pass effect; rather, it is transported across the placenta, exposing the fetus to an adult dose of the drug," Friedman explained.

Although metformin is prescribed during pregnancy to lower the risk of diabetes-related complications, such as obesity and diabetes in children, the study suggests that the drug itself may contribute to these same risks.

"Given these results and the prevalence of metformin use during pregnancy, additional investigation of any potential immediate and enduring effects of prenatal metformin use is warranted," the researchers wrote.

Previous research on medications used during pregnancy has mainly focused on whether they could cause harm to the babies. Less attention was given to the effects on their growth and metabolism. While metformin is deemed safe because it has not been linked to birth defects, the researchers note that the fetus lacks a way to fully clear the drug from its system.

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