Metformin Use During Pregnancy Doesn't Increase Birth Defect Risk

Two recent studies provide reassurance that the diabetes medication metformin is safe to use before and during pregnancy, posing no increased risk of birth defects. These findings apply to both men planning to conceive with their partners and women in early pregnancy, contradicting a 2022 study that suggested metformin use by men three months before conception was linked to a 40% higher risk of birth defects in their offspring.

Dr. Ran Rotem, a key researcher in one of the new studies, emphasized that traditionally, maternal health has been the primary concern during pregnancy. However, recent evidence indicates that paternal health is also crucial. Diabetes, whether in mothers or fathers, presents complexities that can affect fertility and pregnancy outcomes. While lifestyle changes such as increased exercise and dietary adjustments are recommended to manage diabetes, metformin remains a safe medication option if pharmacological intervention is necessary.

Rotem's study scrutinized medical records of nearly 400,000 babies born in Israel from 1999 to 2020, along with relevant paternal information like age, lab results, and medication records. The investigation revealed that the rate of major birth defects was 4.7% among children of fathers who did not use diabetes medications before conception, compared to 6.2% among those whose fathers used metformin. However, when other health conditions and maternal diabetes were considered, the increased risk was not statistically significant. Interestingly, a higher risk was noted when fathers used other diabetes medications alongside metformin, likely due to more poorly controlled diabetes rather than the medications themselves.

The second study, published in the Annals of Internal Medicine alongside Rotem's research, focused on women and reached similar conclusions. This study analyzed Medicaid data on over 12,000 women with type 2 diabetes and their pregnancies. It found that women who continued metformin while adding insulin in the first trimester had no significant increase in the risk of birth defects. The estimated risk for birth defects was about 6% when mothers used both insulin and metformin, compared to 8% when only insulin was used.

Dr. Yu-Han Chiu, a researcher involved in the second study, explained that although metformin can cross the placenta, its role in better blood sugar control may lower the risk of birth defects. Poor blood sugar control is a known risk factor, and combining insulin with metformin may offer better management of blood sugar levels than insulin alone, contributing to the observed lower risk of birth defects.

Dr. Sarah Martins da Silva from the University of Dundee in Scotland commented on the significance of these findings in an editorial. She suggested that these studies highlight metformin as a safe and effective treatment for type 2 diabetes for both men and women attempting to conceive, as well as for managing high blood sugar in pregnant women during the first trimester. This new evidence may prompt a reevaluation of current prenatal care guidelines that recommend switching from metformin to insulin therapy.

These recent analyses underscore the importance of metformin as a viable option for managing type 2 diabetes in the context of conception and pregnancy, providing critical information for future prenatal care recommendations.