Animal study raises questions about semaglutide safety during pregnancy

They're the blockbuster drugs transforming weight loss, helping millions of people to shed unwanted kilos. But while medications such as Ozempic and Wegovy may also improve women's chances of falling pregnant, what happens to their unborn babies if they continue to take the drugs during pregnancy?

In a new Adelaide University animal study involving pregnant sheep, researchers found that semaglutide – the active ingredient in these medications – significantly reduced blood flow to the uterus and oxygen levels in the developing fetus.

While the findings are preliminary and have not been demonstrated in humans, they raise important questions about the safety of weight-loss drugs during pregnancy, particularly for women who may conceive unexpectedly or continue taking the medication before realizing they are pregnant.

Semaglutide is not recommended during pregnancy (and women planning to conceive are advised to discontinue treatment beforehand) researchers say many will be reluctant to discontinue treatment to avoid regaining lost weight, while others taking the drug to manage diabetes may have concerns about changing their treatment.

The new research, published as a conference abstract in the journal Heart, Lung and Circulation, is helping researchers better understand the effects of the GLP-1 medications into late gestation in order to better understand how they might affect a developing fetus.

Adelaide University researcher Dr Mitchell Lock said the potential effects of semaglutide taken during pregnancy remain poorly understood.

While weight-loss medications have become incredibly popular, there's still a lot we don't know about how they might affect a developing baby.

In this study we wanted to understand what happens to the mother's cardiovascular system and the blood and oxygen supply to the fetus when semaglutide is administered during pregnancy.

Within two hours of administering semaglutide, we found that the amount of blood pumped by the mother's heart had significantly decreased, reducing blood flow to the uterus and lowering oxygen levels in the developing fetus.

Oxygen is essential for healthy fetal growth and development, so any reduction in its supply raises questions about what might happen if exposure to the drug continues throughout pregnancy."

Dr. Mitchell Lock, researcher, Adelaide University

The sheep study used advanced magnetic resonance imaging (MRI) to measure maternal heart function and blood flow to the uterus before and after administering semaglutide. Researchers collected fetal blood samples and monitored blood pressure and heart rate to assess the drug's immediate effects on the developing fetus.

In Australia, around half a million people use GLP-1s for diabetes, yet their weight loss properties suggest this is likely much higher. In the US, about 12% of adults use GLP-1s for weight loss.

Senior researcher, Professor Janna Morrison said the findings highlight the need for further investigations into the potential effects of prolonged exposure to semaglutide during pregnancy.

"Our findings suggest a potential risk to fetal development, but we haven't yet established whether these short-term changes affect fetal growth, what happens over a longer period of semaglutide use or whether similar effects could occur in human pregnancies," Professor Morrison said.

"With the growing popularity of GLP-1 medications, it's important that we better understand their potential effects during pregnancy so women and healthcare professionals can make informed and safe decisions about their use."

Semaglutide is not recommended during pregnancy, and women planning to conceive are advised to discontinue treatment beforehand.