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ATLANTA — 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.
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 polycystic ovary syndrome, 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 act by mimicking hormones in the gut involved in insulin regulation and appetite. They're both approved to treat Type 2 diabetes, and each has twin medicines approved for weight loss.
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 these 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 polycystic ovary syndrome 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 the research behind these medicines.
"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 the 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 these 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 this type of drug 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.
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.
–Dr. Daniel Skovronsky, Eli Lillly
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 the drugs may reduce the number of proteins that are responsible for transferring nutrients from the mother to the fetus, often found in the placenta.
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 the class of 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 these 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.
