A large study from Harvard T.H. Chan School of Public Health offers reassuring news for pregnant women who have continued taking GLP-1 receptor agonists—the popular weight-loss and diabetes medications—into their first trimester. Researchers analyzing insurance claims data from 3,572 pregnancies between 2011 and 2024 found that continuing these medications after conception did not substantially increase risks for miscarriage, abnormal fetal growth, or major birth defects.
The finding arrives as GLP-1 receptor agonists, including drugs like semaglutide and tirzepatide, have become increasingly common among women of reproductive age. With more women using these medications, questions about their safety in pregnancy have grown urgent—particularly for those who discover they're pregnant while already taking them. This study, published in the Annals of Internal Medicine, provides the first large-scale evidence comparing what happens when women continue these medications versus those who stop them.
Researchers from Harvard conducted what's called a "target trial emulation," a research method that mimics a randomized controlled trial using real-world data. They compared two groups: women who received at least one additional GLP-1RA prescription after conception and continued into the first trimester, and those who did not continue the medication. The analysis examined outcomes including nonlive birth, abnormal fetal growth, and major congenital malformation—the most serious concerns clinicians and patients face.
The results showed similar risks between the two groups for most pregnancy outcomes. The researchers found no definitive increase in adverse outcomes for women who continued taking GLP-1RAs into the first trimester. This finding is particularly important because many women take these medications for type 2 diabetes or weight management without initially realizing they're pregnant, leaving them with a critical decision about whether to stop suddenly or continue treatment.
However, the researchers were careful to note limitations in their study. Because major congenital malformations and small size for gestational age are relatively rare outcomes, the estimates for these specific conditions were imprecise—meaning larger studies would be needed to rule out risks entirely. "The findings can provide some reassurance for pregnant women with unintentional first-trimester exposure to GLP-1RAs," the researchers wrote, while acknowledging that further research would be valuable to better understand the full safety profile of these medications across pregnancy.
The distinction between intentional continuation and accidental exposure matters enormously for clinical practice. Women who discover they're pregnant while on GLP-1RAs can now discuss their options with more confidence, knowing that the available evidence does not suggest they must immediately stop taking medication that may be essential for managing their health. At the same time, the researchers' call for additional studies reflects the responsible scientific approach: reassurance based on current evidence, but acknowledgment that our understanding will continue to evolve as more data accumulates.