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Researchers set out to check the safety of using weight loss jabs during pregnancy, and came across a worrying finding in their animal-based study.
Experts at Adelaide University, Australia, gave semaglutide—the active ingredient in weight loss jabs—to seven pregnant sheep and they found the GLP-1 could have a concerning impact on their bodies.
They found notably decreased blood flow to the uterus and reduced oxygen levels in the developing fetuses within only two hours of the pregnant sheep being administered the weight loss drug.
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An abstract of the study was published in the journal Heart, Lung and Circulation in August. The full study has not yet been published.
The researchers say that while the results have not been validated in humans and pregnant women are already advised not to take GLP-1s, they raise important questions about the safety of weight loss drugs during pregnancy, particularly for women who conceive unexpectedly.
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What The Study Found
Near the end of the sheep's pregnancies, the researchers gave them a single dose of semaglutide and then measured changes in both the mother and fetus.
The sheep were assessed between 113 and 116 days gestation (the period of time the fetus develops in the uterus). A sheep is typically pregnant for around 147 days before birth.
They found that within less than two hours of infusion, the amount of blood pumped by the mother's heart significantly decreased, resulting in reduced blood flow to the uterus and lower oxygen levels for the fetus.
They said that this raises concerns over what could happen to a mother and fetus over a longer period of time if semaglutide is taken during pregnancy, as stable blood flow and oxygen levels are essential for the health of a developing fetus.
How Could Semaglutide Have This Effect?
Study author Mitchell Lock, a research fellow at Adelaide University, told Newsweek that it is "currently unknown what causes this change in blood flow."
"We are performing further investigations to determine the mechanism in a separate animal study looking at chronic use of the drug," he said.
However, he added that they hypothesize that "the maternal uterine vasculature expresses the GLP-1 receptor," and that "this change is due to alterations in maternal blood flow following action on these receptors."
He also said that "we don’t believe there is a direct effect on the fetus," as it is currently thought that "semaglutide does not cross the placenta due to the size of the molecule."
What Do The Findings Mean?
Lock said that it is currently "not recommended to use semaglutide during pregnancy—the manufacturers and clinical guidelines recommend to stop taking the drug two months prior to conception."
"However, there are problems with this recommendation," he added. "Weight loss while on the drug is known to increase fertility and many women may not even know they are pregnant while on the drug."
"We need to know more about what happens in these cases so that clinicians have the best available evidence for their patients," he said.
He added that more animal studies are "currently underway to better understand the mechanism of how this happens and what it means for both mother and baby."
He emphasized that while their preliminary evidence has shown some possible negative effects of the drug, it is "important to note that we don’t know if this same response occurs in humans yet."
He said that there is a "current lack of medications available for use during pregnancy, causing a health gap for these women."
"There is much interest in the use of GLP1 agonists during pregnancy for other conditions such as controlling gestational diabetes," he said. "Only by researching these drugs further will we know the possible positive or negative reactions to the drug on maternal and fetal health."
Reference
Cho S, Lock M, Holman S et al. (2024) Do Weight Loss Drugs Impair Fetal Growth? Heart, Lung and Circulation. https://www.heartlungcirc.org/article/S1443-9506(26)01387-9/fulltext
Contact Newsweek editors on this story: Kara Dolman and Paul Donnelley.
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