Prescription Drugs in Pregnancy and Congenital Malformations: A Population-Based Safety Screening Study

Counseling women who are either pregnant or contemplating pregnancy on their use of prescribed drugs remains a major clinical challenge. Since the thalidomide tragedy in the 1960s, the use of drugs during pregnancy has been subject to widespread concern due to the potential for unwanted effects on the unborn child, notably major congenital malformations.

To examine the risk of major congenital malformations following first trimester exposure to all marketed prescription drugs in Denmark.

This was a population-based cohort study utilizing national health registries in Denmark. We studied all singleton livebirths in Denmark between January 1, 2004, and December 31, 2017, and we linked data from the National Danish Prescription Register, Birth Register, Patient Register, and Cause of Death Register. Using logistic regression analysis, we compared exposed liveborn to unexposed liveborn children while controlling for important confounders. The main outcome measure was major congenital malformations, and the secondary outcomes included organ-specific major congenital malformations as defined by EUROCAT.

Of 326 drugs with at least 5 livebirths with major congenital malformations, 31 were associated with an increased risk of major congenital malformations compared to unexposed livebirths (adjusted Odds Ratio [aOR] ≥ 2.0). Compared to livebirths of women who discontinued treatment prior to pregnancy, 17 drugs with an increased risk (aOR ≥ 2.0) were identified. Among 115 drugs prescribed to ≥ 1000 women during the first trimester, only insulins had aORs ≥ 2.0 for overall major congenital malformations. There were > 100 drugs with no increased risk of major congenital malformations.

Using a complete nationwide dataset, > 100 null-associations between first-trimester drug exposure and overall major congenital malformations were documented. This provides important insights and reassurance to support pregnant women and inform shared decision making. We confirm previously known teratogenic drugs and other potential teratogenic drugs, clopidogrel and liraglutide, were identified. These latter associations should be addressed in future studies using disease-specific confounder control.