Potential fathers with type 2 diabetes can be reassured that taking the drug metformin is not associated with birth defects in their offspring, concludes a large study of more than 3 million pregnancies published by The BMJ today. The researchers say the findings show that metformin can continue to be considered a suitable drug for managing blood sugar levels in men with type 2 diabetes who plan on having children. Metformin is widely used to treat type 2 diabetes in men of reproductive age, but a recent Danish study reported a link between metformin use by fathers-to-be and an increased risk of congenital malformations, particularly genital, in male infants.
However, questions about the biological plausibility and causality between paternal metformin use and risk of congenital malformations in offspring remain unresolved. To provide further guidance on this issue, researchers set out to evaluate the association between paternal metformin use and risk of congenital malformations in offspring from Norway and Taiwan. Using national birth registries and prescription databases, they identified 619,389 offspring with paternal data during the period of sperm development (three months before pregnancy) in Norway during 2010-21 and 2,563,812 in Taiwan during 2004-18.
Among these, fathers of 2,075 (0.3%) offspring in Norway and 15,276 (0.6%) offspring in Taiwan used metformin during the sperm development period.
In Norway, congenital malformations were found in 24,041 (3.9%) offspring.
