The use of a first-line oral diabetes drug, metformin, during sperm production has now been linked to the increased risk of birth defects. According to the study published last week in Annals of Internal Medicine, genital birth defects are 3.39 times more likely in the offspring of men who consumed metformin during the 90 days prior to conception. All of these genital birth defects occurred in male offspring.
Researchers in Denmark and at Stanford University looked for the risk of birth defects in more than 1.2 million births in Denmark from 1997 to 2016. Due to the country’s comprehensive medical registries, they obtained individual-level data on birth defects, parental drug prescriptions, and confounding variables such as parental age and maternal medical history.
Remarkably, there was no association to birth defects if metformin was used outside of the sperm development window of 90 days prior to conception, nor for insulin or other diabetes drugs used by men. Thus, the effects of metformin on birth defects appear to be restricted to sperm production rather than broad effects. The effect of metformin use by women was not examined since the children of mothers with diabetes were not included in the study.
Follow up research is necessary to confirm these findings and examine the underlying mechanism. Given the high prevalence of diabetes, understanding the effect of medications, nutrition, and physical exercise, both in the context of conception and of disease management more broadly, is important for improving health outcomes.