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Does Using Metformin During Pregnancy Cause Birth Defects?

Metformin and gestational diabetes

Metformin is used primarily for type 2 diabetes but is also used in gestational diabetes; Gestational diabetes is a blood sugar-related dysfunction that develops during pregnancy. Within the last decade, increases in diagnoses of diabetes amongst young adults have been matched by an increase in the use of metformin during pregnancy. Researchers investigated whether using metformin during pregnancy leads to birth defects.

Does metformin cause birth defects?

It is known that metformin crosses the human placenta exposing the baby to the medication. This drug can affect cell function in the growing fetus but it is unknown whether this exposure leads to birth defects.

Previous studies have found no evidence that metformin causes birth defects. However, these studies included a small number of participants and were not well-designed. To address the faults of previous studies, researchers at the Administrative Data Research Centre in Northern Ireland conducted a large, international study to investigate whether metformin exposure during pregnancy causes birth defects.

The researchers collected data from over 50,000 babies with birth defects. The risk of birth defects was increased if the mother was diabetic. However, the risk of birth defects was not increased in women with infertility or polycystic ovary syndrome. Only 168 babies in the study were exposed to metformin through the mother’s placenta.

The researchers found no evidence of an increased risk of birth defects in the babies exposed to metformin. The only birth defect that remained significant after the statistical analysis was pulmonary valve atresia, a specific abnormality of the heart. This type of birth defect is associated with diabetes and may not be associated with medication exposure. Also, the low number of cases of this type of birth defect might also suggest that it occurred by chance.

Results of the study

The researchers did not find an increase in birth defects in babies born from women who were taking metformin during pregnancy. Also, it is worth noting that studies involving pregnant women using metformin are always complicated because if a mother’s blood sugar is not controlled during pregnancy, she is putting her baby at risk of birth defects.

Abnormalities that were detected in babies whose mothers used metformin were likely due to chance. Further studies are required to confirm the low risk or absence of risk of cardiac abnormalities in babies exposed to metformin during pregnancy.


  1. Given JE, Loane M, Garne E, et al.Metformin exposure in first trimester of pregnancy and risk of all or specific congenital anomalies: Exploratory case-control study. BMJ. 2018. https://doi.org/10.1136/bmj.k2477
  2. Friel, LA. Diabetes Mellitus in Pregnancy. Merck Manual. https://www.merckmanuals.com/en-ca/professional/gynecology-and-obstetrics/pregnancy-complicated-by-disease/diabetes-mellitus-in-pregnancy
  3. Pinkerton, JV. Polycystic Ovary Syndrome (PCOS). Merck Manual. https://www.merckmanuals.com/en-ca/professional/gynecology-and-obstetrics/menstrual-abnormalities/polycystic-ovary-syndrome-pcos

Jessica Caporuscio PharmD
Jessica Caporuscio PharmD
Jessica received her Doctorate of Pharmacy from the University of Montreal in July 2014 and she has been working as a community pharmacist in the Greater Toronto Area since March 2015. She has a passion to communicate medical and drug information to her patients and other healthcare professionals. Jessica is also a marathoner and an Ironman triathlete. In her spare time, she is in her kitchen creating healthy recipes for her family.


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