When Sarah Carter was pregnant with her first child, she started digging into the research on ultrasounds, scouring studies in mice and rats. She couldn’t find any evidence in humans they cause harm — professional groups agree that ultrasounds are helpful and safe to perform during pregnancy.

But Carter didn’t see any studies that explicitly showed they were safe. Then, she heard something that compounded her concerns. After an ultrasound, a friend of a friend was told her fetus had a limb malformation. She spent her pregnancy riddled with anxiety, only to find out nothing was wrong after the baby’s birth.

Carter decided to refuse every ultrasound while pregnant. To her, the idea of spending her pregnancy anxious about ultrasound results seemed risky — riskier than the chance of missing something rare, but important, on a standard scan. When her birthing center told her an ultrasound was mandatory to deliver there, she found a new provider.

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“I felt they were forcing my hand and not letting me make my own decision,” said the 38-year-old art therapist. “I wanted to trust my body.”

Carter’s decision reflects a debate among some women about whether to forgo ultrasounds altogether, a question that has cropped up on social media groups for pregnant women and pregnancy and parenting blogs. And while health care providers agree it’s a woman’s choice whether to have a scan, they worry about women skipping all of them. Ultrasounds are key to screening for serious developmental problems — including some that can be addressed in utero. Ultrasound results can dictate whether a woman needs to give birth at a certain kind of facility, so that specialists are on hand to care for the baby after birth. They can tell providers and women whether they’re carrying twins, or whether their placenta is too low or their baby is breech as labor begins.

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Prenatal care providers who spoke with STAT reported varying numbers of patients who refused ultrasound. Some often encountered skepticism, while others more frequently cared for women who were on the opposite end of the spectrum: getting far more ultrasounds than they needed at new standalone clinics that offer 3D and 4D scans. All of them suggested the deviations from recommended scans were a new cause for concern.

“It’s pretty scary that there are some women out there who have no ultrasounds during pregnancy, because we really rely on it as a screening and diagnostic tool,” said Dr. Leena Nathan, an obstetrician-gynecologist at UCLA Health.

Ultrasounds use sound waves to capture images of a fetus inside the uterus. Many women have ultrasounds during the first trimester, which is helpful to estimate how far along a pregnancy is. Several providers told STAT they aren’t troubled by women who skip that “dating” scan. But they strongly recommend all women have what’s known as the anatomy scan, or an ultrasound around 20 weeks gestation to look at fetal development and check for any problems. Some women — including those with high-risk pregnancies or women carrying twins — have more scans.

Ultrasounds have been used to monitor pregnancy for decades, and there’s no meaningful evidence that they can cause harm to a developing fetus. The American College of Obstetricians and Gynecologists notes that “no links have been found between ultrasound and birth defects, childhood cancer, or developmental problems later in life.”

But experts can’t rule out the possibility that future research could point to possible effects, which is why they recommend that pregnant women only get ultrasounds that are necessary and are performed by trained providers as part of their prenatal care.

“We know that it’s safe to the degree that nearly every person gets one or two scans in their pregnancy, and we haven’t seen any untoward effects,” said Nathan.

But some women still want to avoid them, like Erin Rice Petrillo, a 36-year-old from Pennsylvania. Pregnant with her first child in 2015, Petrillo took a birthing class where her teacher shared a traumatic birth experience in the hospital. That story pushed Petrillo to seek out other women’s stories. She started reading the research on prenatal care and poring over articles on her choices as a pregnant woman.

She set out to find a provider who would be on the same page as her when it came to her prenatal care. She ended up selecting a midwife who practiced at a hospital, hoping she might support Petrillo in declining some kinds of standard care, like ultrasounds. Petrillo knows that experts recommend the scans during pregnancy when it’s medically necessary. But she didn’t feel that the scans were necessary for what she saw as a “routine pregnancy” without any problems.

Petrillo firmly believes that pregnancy isn’t a medical condition, but a natural state for a woman’s body. Unnecessary medical procedures, she said, can lead to a “cascade of treatments, tests, or procedures” that also aren’t necessary.

“My philosophy is that your body is gonna do what it’s gonna do. Hearing the heartbeat super early or seeing whatever development early on, it’s not going to change the outcome,” she said.

It wasn’t a clear-cut choice. Petrillo hesitated, in particular, about skipping the 20-week scan, knowing it could catch some problems that, if discovered before birth, would warrant intervention in utero or right after a baby’s birth.

“I questioned myself making that decision the most,” she said. Ultimately, Petrillo didn’t have ultrasounds while pregnant with either of her children, born in 2016 and 2019. She said she would have reconsidered that decision if there were any signs of serious complications.

Prenatal care providers often field questions from pregnant women about the potential risks of ultrasounds. They walk women through the evidence, emphasize the benefits of ultrasound, and lay out the risks of skipping a scan. They make it clear that forgoing the scans can leave women and providers in the dark about certain problems, like a heart malformation or underdeveloped kidneys.

“When we find things with ultrasound, we can counsel the parents about what to expect, make all kinds of plans for newborn care, and make sure the baby is born in a place that can take care of those problems right away,” said Dr. Celeste Sheppard, a maternal-fetal medicine specialist at the University of Texas at Austin.

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It’s a delicate balance for providers. They want to hear out a woman’s questions and concerns. They don’t want to downplay a woman’s worries or strong-arm her into having a scan she doesn’t want to have. But they do want to make sure women are armed with accurate information.

“These are long conversations that you have to take the time to have, to make sure the family understands the provider’s concerns and the benefits [of an ultrasound],” said Shadman Habibi, a nurse-midwife at UCLA Health.

If a woman decides to abstain from ultrasounds, Sheppard said, “that’s her prerogative.” She would continue to care for that patient and avoid “an arm wrestle” about the question of ultrasounds. But Sheppard said she understands why some providers might dismiss a patient from their practice if she refuses any scans.

“It’s also the prerogative of the physician to say ‘Well, OK, I can’t see you anymore … I’m happy to help you find someone else,’” said Sheppard, who is also the clinical director of ultrasound at UT’s women’s health department.

Several providers said they see women having too many ultrasounds more often than they see women skipping the scans altogether.

“Usually, people want more ultrasounds and we’re trying to talk them out of ultrasounds,” said Dr. Chemen Neal, an obstetrician-gynecologist at Indiana University Health.

The fast-growing business of 3D and 4D ultrasound centers has fueled that trend. Some clinics offer package deals, bundling multiple scans at different stages of pregnancy. Others tout a discount or keepsakes if women come back for more ultrasounds.

“It’s become a cultural norm,’” said Carter, one of the women who opted to have no ultrasounds.

And all those extra ultrasounds have providers worried. While there is no evidence that ultrasounds pose a risk to developing fetus, it isn’t clear whether there are any risks with excessive ultrasounds. ACOG cautions against the “casual use of ultrasound.”

“All of our professional societies — and I as well — have some concern about unregulated use of medical ultrasounds,” Sheppard said.

Among those concerns: the scans aren’t necessary and the people providing them might not be trained to stick to medical guidelines, like operating the ultrasound machine at too high a power setting or using it for longer than recommended.

Providers are also concerned about the possibility of an ultrasound technician at a freestanding clinic missing a problem with a pregnancy, giving a woman a false sense of security. Sheppard pointed to a case in which a fetus had a hole in its abdominal wall, leaving its intestines growing outside the body — a problem missed in an ultrasound at a 3D/4D clinic.

“When a mom is falsely reassured, I think [that] is harmful and concerns me,” said Sheppard.