'Ozempic babies': What the science says on whether GLP-1s lead to surprise pregnancies

Catera Bentley stared at the positive pregnancy test and couldn't believe her eyes. She took a second test, then a third - there was no question. She was pregnant.

She called her husband at work and told him that there was a giant spider in the house that he had to come get rid of. He rushed home, and when he arrived, Bentley revealed the news. They both burst into tears.

The couple, who live in Steele, Alabama, had been trying to have a child for more than two years, but Bentley's doctor had told her that she may be unable to conceive because of her history of polycystic ovary syndrome, known as PCOS.

The news had left her feeling without a purpose. "That's all I wanted to be was a mom and a wife," said Bentley, 25. "I was depressed, severely depressed for that whole time."

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Five months earlier, in October 2022, Bentley had started taking Mounjaro for weight loss. Over the first few months, she said, she lost about 40 pounds. Her menstrual cycles, which had been irregular because of PCOS, became normal. And she even felt happier.

"It just made me feel like a whole new person," she said. "I was in a better mood every single day."

Bentley had hoped that losing weight might help her get pregnant, and she'd heard about others having success with weight loss while taking the shot. But when she did become pregnant - sooner than she expected - she worried about the effects it might have on her baby.

'Ozempic babies'

Bentley is far from alone. Numerous women have shared stories of "Ozempic babies" on social media. But the joy some experience in discovering pregnancies may come with anxiety about the unknowns, as these medicines haven't been studied in people who are pregnant.

"We don't know the effect of early exposure ... on the fetus," said Dr. Jody Dushay, a physician focused on endocrinology and metabolism at Beth Israel Deaconess Medical Center and an assistant professor at Harvard Medical School.

Dushay said she recommends that women stop taking these drugs two months before trying to get pregnant, as directed in their prescribing information.

Ozempic and Mounjaro are part of a class of drugs called GLP-1 receptor agonists, which act by mimicking hormones in the gut involved in insulin regulation and appetite. They're both approved to treat type 2 diabetes, and each have twin medicines approved for weight loss. Ozempic uses the active ingredient semaglutide, and Wegovy is the version approved for weight loss. Mounjaro uses tirzepatide, which also targets a second hormone called GIP, and Zepbound is its brand name for weight loss.

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The medicines have been shown to help people lose 15% to 20% of their body weight, on average, in clinical trials.

And because of the way GLP-1 drugs work, experts say, there are reasons they may lead to more pregnancies as well as cause for caution about their use in early pregnancy.

An effect on birth control

For one, weight loss can generally be associated with increased fertility by restoring normal ovulation in people who have PCOS or other causes of abnormal cycles, said Dr. Daniel Drucker, a professor and researcher at the University of Toronto's Mount Sinai Hospital and a pioneer of research into GLP-1.

"If you start on these medicines and then you lose 5, 10, 15% of your body weight, very often, you will have an improvement in ovulation," Drucker said.

One scenario that's "quite conceivable," he said, is that someone who has obesity and doesn't have frequent menstrual periods starts one of these medicines, loses weight over several months and finds that they're still not having regular periods - "only now it might be because you're pregnant."

On top of that, Mounjaro and Zepbound have a warning in their prescribing information that they may render birth control pills less effective.

Drucker said this may be because the drugs work in part by slowing the rate at which food moves through the stomach. This can make people feel full for longer but also could interfere with absorption of other medicines, including birth control pills.

Mounjaro and Zepbound warn about this explicitly on their labels, but Ozempic and Wegovy only warn more broadly about absorption of any drugs taken by mouth.

Safety in pregnancy

Even as GLP-1 medicines may increase fertility, little is known about their safety during pregnancy. The drugs' makers, Novo Nordisk and Eli Lilly, excluded people who were pregnant or planned to become pregnant from their clinical trials, a common practice when testing new medicines.

But that doesn't mean there's no information available.

"The more these meds are used, the more women will get pregnant while taking them, and we will in that way accumulate data on risk of early pregnancy exposure," Dushay explained. In other words, "we basically gather data from 'accidents' as we do for most drugs."

The few studies available about babies whose mothers took GLP-1s early in pregnancy haven't turned up major causes for concern, although researchers note that more study is needed - and it's underway.

Novo Nordisk has a registry where it's collecting data about the safety of Wegovy during pregnancy. A company spokesperson says the findings will be disclosed at the end of the study. An entry on a government database on clinical trials notes that the study plans to enroll more than 1,100 participants and is expected to be completed by the summer of 2027.

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An Eli Lilly spokesperson said the company also plans to open a pregnancy registry for Zepbound, which was approved at the end of last year.

Studies in animals, though, have suggested some cause for caution, Drucker said.

"If animals get high doses of these drugs, very often, the babies that are born to the mice and rats are small, and sometimes, they have some malformations," he noted.

That's probably because the drugs also work by reducing appetite.

"If you restrict energy intake in a pregnant animal, then the baby's not going to get enough nutrients and won't be able to grow properly," Drucker said.

He also pointed to a study in animals suggesting that GLP-1 drugs may reduce the number of proteins that are responsible for transferring nutrients from the mother to the fetus, often found in the placenta.

Already in use for PCOS

Those concerns complicate research on the medicines for infertility, but some work is ongoing on one of the most common causes: PCOS. The condition affects as many as 12% of women of reproductive age in the United States, according to the US Centers for Disease Control and Prevention.

The exact cause of PCOS is unknown, but it's associated with excess weight, which is thought to contribute to the body's production of too much insulin. That, in turn, results in hormonal imbalances - specifically, higher levels of hormones like testosterone, which can stop ovulation and cause irregular periods, acne and excess facial hair, according to the CDC.

Although there's no cure, weight loss alone can lead to significant improvement of symptoms and resumption of regular ovulation and menstruation, said Dr. Anuja Dokras, director of the PCOS clinic at the University of Pennsylvania.

Lifestyle changes are the first-line treatment for PCOS, but if those interventions aren't successful, doctors may prescribe Ozempic or other GLP-1 agonist medications, Dokras said. The 2023 international PCOS guidelines list GLP-1 agonists among the medications for "management of higher weight in adults with PCOS."

GLP-1 agonists improve insulin resistance and lead to weight loss, so it makes sense that they also improve PCOS symptoms, added Dr. Melanie Cree, director of the multidisciplinary PCOS Clinic at Children's Hospital Colorado.

"It is completely being used now with no evidence because the [obstetrics] field knows that if you have 5% weight loss in these individuals with PCOS, you will improve fertility," she said.

Cree noted that studies have shown that liraglutide, an earlier GLP-1 drug sold as Victoza for type 2 diabetes and Saxenda for weight loss, is effective at reducing body weight and testosterone levels in women with PCOS and obesity.

Cree also just wrapped up a clinical trial investigating the use of semaglutide, the active ingredient in Ozempic and Wegovy, for PCOS treatment in adolescent girls. The preliminary findings, which have not been published, showed that both semaglutide and a low-sugar diet resulted in more frequent periods, lower testosterone levels and weight loss - and the weight loss was much more pronounced in the group taking semaglutide.

Regardless of the method, the study found, people who lost more weight had greater decreases in testosterone levels.

Cree is now running a larger and longer clinical trial, funded by the National Institutes of Health, that will look specifically at fertility outcomes for young women with PCOS who take semaglutide.

And while the drugs' makers aren't currently running trials in PCOS - which Cree attributes in part to the fact that PCOS overlaps so much with obesity that it wouldn't dramatically expand the market for the medicines - approval for the condition, she pointed out, could have an important effect on insurance coverage, which is challenging for many people using them for weight loss.

"For example, Colorado mandates fertility coverage, so if it was approved as a fertility medication, then it would be covered for that indication," she said.

Separately, Cree pointed to another question about the medicines during pregnancy: the potential for quick weight regain that can happen when patients stop them suddenly.

"If that's happening in the setting of pregnancy, when you're gaining all this weight, what happens?" she said. "What does that mean? And we just don't know."

A 'Catch-22'

The drugs' makers are also following the "Ozempic babies" phenomenon. Eli Lilly's chief of research, Dr. Daniel Skovronsky, says the company has heard these kinds of stories from patients.

"One question we're asking is: is it possible that as we reduce fat, we improve fertility, decrease PCOS and other barriers to fertility?" Skovronsky said.

"It's kind of like heart failure or sleep apnea," he said, referring to conditions for which GLP-1 drugs have recently shown positive results. "Just another potential benefit of weight loss from this class of medications that we haven't tested yet."

He also underlined how tricky it is to run studies around fertility of medicines whose safety in pregnancy is unknown; Cree referred to a requirement for birth control in studies of GLP-1 drugs as a "Catch-22" for fertility indications.

"Right now, unfortunately, it's really hard to study the effects of these drugs on fertility, because that implies exposing women to a drug with a high risk that they'll have a pregnancy during exposure to the drug and the risks to the baby haven't been fully analyzed yet," Skovronsky said.

Bentley, who got pregnant while taking Mounjaro, said she stopped taking the medicine as soon as she found out she was pregnant. But she said she continued to worry about the effect of the drug on her baby.

"I worried up until the day I had her," she said.

Her daughter, Ivy, was born healthy on her due date, weighing 7 pounds and 7 ounces. Bentley started taking Mounjaro again six weeks after Ivy was born.

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