Harvard Doctors See No Birth Defect Spike From Ozempic, Still Flash Caution Light

A new Harvard analysis is offering some cautious relief for people who stayed on GLP-1 weight-loss drugs such as semaglutide in very early pregnancy. The study found that continuing these medications into the first trimester did not appear to increase the risk of major birth defects or several other common adverse outcomes. The findings are reassuring for patients who were unknowingly exposed, though they do not rule out the possibility of rarer problems.

What the study looked at

Researchers used a "target-trial emulation" design to line up two groups of pregnancies: one in which GLP-1 receptor agonists were continued into the first trimester and another in which the drugs were stopped. The team analyzed 3,572 pregnancies recorded between 2011 and 2024, according to Annals of Internal Medicine.

What researchers found

Investigators did not see a statistically meaningful increase in non-live births, and they found no clear uptick in major congenital malformations or in markedly abnormal birthweight distributions. The weighted risk of non-live birth was about 29.7% with medication continuation compared with 27.1% when the drugs were stopped. The authors stressed that estimates for rarer outcomes were imprecise, as reported by Reuters.

Doctors still urge caution

Clinicians in Boston and beyond say the paper offers some reassurance for accidental early exposure, but not a green light to stay on GLP-1s during pregnancy. Current guidance still recommends stopping these drugs about two months before trying to conceive, and senior author Sonia Hernández-Díaz cautioned that "our study cannot on its own change such recommendations," according to CBS News.

How this fits with earlier research

The new Annals analysis lands in the middle of a mixed evidence base. A 2025 Mass General Brigham study in JAMA reported that people who stopped GLP-1 therapy before or early in pregnancy had greater gestational weight gain and higher risks of preterm delivery, gestational diabetes, and hypertensive disorders of pregnancy. That earlier work highlights the trade-offs clinicians have to weigh when advising patients, as outlined in JAMA.

Bottom line for patients

For patients, the practical takeaway is fairly straightforward: inadvertent first-trimester exposure to GLP-1 drugs appears less likely to signal a major birth-defect risk, but it is not a free pass. Individual counseling and monitoring remain key. The authors and outside experts are calling for larger studies to clarify risks for rarer outcomes and continue to advise women to speak with their obstetrician or prescriber about contraception and pregnancy planning, according to a summary from the American College of Physicians/Annals.