Babies of Fathers Who Take Metformin Are More Likely to Have Birth Defects

Specifically, there's an increased risk of genital defects in those assigned male at birth.

a dad holds his baby on his lap
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A new study from a team of researchers at the University of Southern Denmark and Stanford University found a correlation between fathers who took the diabetes medication metformin and the incidence of birth defects in their children.

The study examined records of more than one million newborns, dating from 1997 to 2016. The researchers found that children of fathers who had taken the metformin during the three months before conception were more likely to be born with a congenital disorder, specifically genital defects in those assigned male at birth. (The children’s mothers had no history of diabetes or high blood pressure.)

Metformin is a popular oral medication used to help control Type 2 diabetes; it’s designed to improve the body’s blood sugar metabolism. It works differently than insulin, which is commonly prescribed for both Type 1 and Type 2 diabetes and directly impacts a cell’s ability to use sugar, says Michael L. Eisenberg, M.D., Director of Male Reproductive Medicine and Surgery at the Stanford University School of Medicine and co-author of the study.

To determine the prevalence of congenital disorders in babies born to fathers taking diabetes medications, researchers considered babies whose fathers had refilled a diabetes drug, either metformin, insulin, or sulfonylureas, within three months of conception. They focused on the three-month mark because it takes sperm three months to develop fully. The researchers found no noticeable effect in babies born to fathers who had taken insulin in the three months prior to conception, and too few babies born to dads who took sulfonylureas to adequately measure outcomes for these kids. However, children born to fathers who had taken metformin were more likely to be diagnosed with a birth defect than other children.

“There have been studies to suggest that diabetes can impair semen quality in terms of volume, concentration, and motility,” Eisenberg says. However, more research is needed to establish what the risk is. “Given that this is a single study, we do not think that clinical practice should change yet. However, other studies should be conducted on other populations. If the current findings are confirmed, then perhaps medication modifications could be suggested.”

Men who are taking metformin should discuss their treatment with a physician before trying to conceive. Since untreated diabetes can also affect sperm quality, stopping metformin treatment could also result in fetal health and birth anomalies. Treatment alternatives should be discussed with a healthcare provider.