Women who use weight loss jabs such as Ozempic and Mounjaro around the time of conception face no higher risk of miscarriage or birth defects, a major study found.
Researchers at City St George's, University of London analysed data from more than two million pregnancies to evaluate the safety of the blockbuster weight management and diabetes injections.
The findings contradict official government guidelines that warn women not to take the medications during pregnancy or for two months before trying to conceive.
Government advice currently cautions that there is not enough safety data to know whether the medicines can cause harm to a developing baby.
Study findings and pregnancy risks
Published in the journal Cell Press, the systematic review represents the largest investigation of its kind. The research team analysed data from ten studies involving more than two million pregnancies.
Among those tracked were 8,325 women who had used weight loss jabs in the six months before or after receiving a positive pregnancy test result.
Researchers found that using the drugs around the time of conception was not linked to a significantly higher risk of miscarriage, stillbirth, birth defects, or premature birth.
The study also recorded no increased risk of gestational diabetes or excessive weight gain during pregnancy for mothers who used the injections.
Furthermore, there was no detectable increase in the risk of babies being born unusually small or unusually large compared with pregnancies where mothers had not used the drugs.
Expert reassurance for expectant mothers
Professor Asma Khalil, an expert in maternal fetal medicine at City St George's, University of London and study lead author, said the results provide reassurance for patients.
"The message for patients is that if you discover you were taking one of these medicines before you knew you were pregnant, you should not panic," Professor Khalil said.
"Healthcare professionals are seeing more women who become pregnant while taking medications such as Ozempic and Mounjaro."
"For many women, discovering they were taking one of these drugs before they realised they were pregnant can be a source of enormous anxiety," she added.
"These findings are reassuring and will help clinicians provide evidence-based advice to women who find themselves in this situation."
Current guidelines and study limitations
Despite the reassuring findings, Professor Khalil recommended that women continue to follow recommendations to stop the injections before a planned pregnancy while further data is collected.
The researchers stressed that the findings should not be interpreted as proof that the medications are safe to use throughout an entire pregnancy.
Because the study was observational, it cannot establish cause and effect, and it does not take into account the potential risks of higher doses.
In addition, most of the women involved in the review did not use the jabs for their entire pregnancy, but rather around the time they got pregnant.
Calls for pharmaceutical research
Professor Tricia Tan, an endocrinologist at Imperial College London who was not involved in the research, welcomed the findings while emphasizing that more work is needed.
Professor Tan said further research is necessary so that women can make fully informed choices when managing their health and pregnancy.
She called on the pharmaceutical industry to fund further research into how these medications affect pregnancy, particularly at higher doses.
Additional research would provide women who use the medications to treat obesity with the reassurance they deserve, Professor Tan explained.
Weight loss jabs and fertility mechanisms
Weight loss injections have increasingly been linked to changes in reproductive health. The medications, known as GLP-1 receptor agonists, were originally developed to control blood sugar levels in people with Type 2 diabetes.
Semaglutide, sold under the brand names Ozempic and Wegovy, and tirzepatide, marketed as Mounjaro, mimic natural gut hormones that help regulate appetite and blood sugar.
The drugs have previously been linked to increased fertility, with some doctors in the United States prescribing them off-label to treat polyendocrine metabolic ovarian syndrome, one of the leading causes of infertility.
Fat cells produce oestrogen, which can negatively affect fertility. Losing weight can help restore hormone levels and regulate menstruation, increasing the chances of conception.
However, doctors have also noted reports of women gaining three times the normal pregnancy weight after coming off the jabs.
Rapid weight gain after stopping GLP-1 injections puts mothers at risk of gestational diabetes, a form of high blood sugar during pregnancy that can increase the risk of premature birth, stillbirth, and other pregnancy complications.
