Almost every pregnant woman in the United States carries a smartphone through nine months of daily use, from period trackers to birth videos.
A new systematic review published in the Journal of Exposure Science and Environmental Epidemiology on September 2026 asks what that constant closeness may be doing to the developing baby, and the strongest signal points to the fetal heart.
Researchers from Columbia University Mailman School of Public Health, Cornell University and Johns Hopkins Bloomberg School of Public Health searched PubMed and Web of Science through February 2026 and pulled together 20 studies on mobile phone use in pregnancy.
Some studies found no clear link. Most tied prolonged or intensive use to problems, above all cardiovascular changes in the fetus and shorter gestation.
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What the cardiac studies showed
Four of the 20 studies looked specifically at cardiovascular effects.
In one experimental study of 90 mothers, 10 minutes of phone exposure in later pregnancy was tied to a drop in fetal cardiac output.
In another with 141 mothers, holding an active phone about 20 centimeters (roughly 8 inches) from the abdomen for 10 minutes was linked to changes in fetal heart rate.
Other studies in the review picked up no cardiovascular effects, and the authors caution that the findings are not consistent enough to prove cause and effect.
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A cross-sectional study of 600 women also flagged an association between cell phone use and spontaneous pregnancy loss, with stronger links seen among women who spent more time on calls or juggled several apps.
What counts as heavy use
The review sets the scene with a jump in exposure that is hard to overstate.
Global cellphone users grew from about 500 million in 2000 to 6.4 billion in 2021, and the average person now spends three to four hours a day on the device.
The studies flagging problems tended to focus on prolonged calls, phones held close to the abdomen, or long total daily screen time rather than a quick text.
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The mechanism the researchers describe is radiofrequency electromagnetic fields, the signals phones use to connect.
These do not damage DNA directly. They may still nudge cell signaling and membrane function, and they can raise the temperature of nearby tissue by a small amount, which the authors say could in theory affect blood flow and organ function in the fetus.
Why this is not a settled answer
The review is a summary of existing evidence, most of it observational, and the authors are clear that heavy phone users differ from light users in other ways too.
Sitting more, sleeping less and eating differently could all be doing part of the work.
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As the paper notes, phone use "may serve as a proxy for sedentary lifestyle rather than strictly reflect radiation exposure."
Columbia environmental health scientist Norman Kleiman, one of the authors, framed the takeaway to reporters.
"The rapid evolution of mobile phone technology and the increased frequency and duration of mobile phone use have raised concerns about potential adverse effects of cellphone exposure during pregnancy, underscoring the need to better understand potential risks to the developing fetus," Kleiman said.
He added that "future research should prioritize well-designed cohort studies with standardized exposure assessments to clarify these associations."
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The U.S. Food and Drug Administration still holds that scientific evidence does not show a health danger from the radiofrequency energy emitted by cell phones under current safety limits.
Practical steps the authors suggest
For readers who want to lower exposure while the science catches up, the review points to simple habits: use the speakerphone or a wired headset instead of holding the phone to the head, keep the device away from the abdomen when it is transmitting, and switch to airplane mode when the phone is tucked in a pocket or resting on the belly.
Anyone with questions about specific exposures during pregnancy should raise them with an obstetrician or midwife, who can weigh individual risk factors.
This article is made and published by Mie Hermansen, who may have used AI in the preparation.