Tylenol during pregnancy? Here's why researchers are urging caution.

Researchers are warning that taking Tylenol during pregnancy might have adverse effects on fetal development.

There is growing evidence to suggest that exposure to acetaminophen can cause neurodevelopmental, reproductive and urogenital disorders, but much more research is needed to determine its exact effects, said Ann Bauer, an epidemiologist at the University of Massachusetts Lowell who co-wrote a statement urging precaution during pregnancy.

In the meantime, the authors of the statement, published Thursday in Nature Reviews Endocrinology, are urging caution. Pregnant people should be advised that they should take acetaminophen only when medically indicated, in consultation with physicians, and in the lowest possible doses, for the shortest time possible, the authors said.

“The evidence supports that we have reasons to be concerned,” Bauer told USA TODAY. She added that “this is not cut-and-dry. We can’t say don't ever use acetaminophen.”

Acetaminophen is the active ingredient in more than 600 pain-relieving medications, including Tylenol. It is also widely used during pregnancy. Studies show that 65% of Americans take acetaminophen while pregnant, compared to about 50% worldwide.

Only about one-third of uses during pregnancy are for urgent needs such as fever or severe pain, Bauer said.

That’s partly because other pain-relief medications are contraindicated during pregnancy, leaving few options. Acetaminophen may still be the best option during pregnancy for some, Bauer said.

“We don’t want to try and scare anybody ... but we want to see that 65% go down,” she said.

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The authors, supported by 91 other scientists and clinicians, reviewed animal- and human epidemiological-based research spanning more than two decades, and came to the conclusion that a precautionary approach was warranted during pregnancy.

The studies indicated exposure to acetaminophen, also known as paracetamol, could be linked to conditions such as ADHD, fertility issues or hormone imbalances, among others.

For the most part, researchers were able to control for other factors that might be causing the higher rates, such as the conditions acetaminophen was taken to treat like fever. But further research with more accurate tracking of levels of exposure to acetaminophen during pregnancy — and also in infants — could be more conclusive, Bauer said.

Additionally, studies done in animals support the conclusion that exposure during pregnancy may be having adverse effects, particularly later on in pregnancy, Bauer said.

The authors are calling on regulatory bodies like the Food and Drug Administration to review the available data to make evidence-based advisements on the risks.

They want more education for physicians, so that they can in turn educate pregnant women about the concerns. Just as doctors advise avoiding alcohol, caffeine and mercury during pregnancy, they should also direct pregnant patients to steer clear of acetaminophen if possible, the authors wrote.

The risks are “fairly modest” for short-term exposure, Bauer said, so the main concern is with longer usage.

“We want women to be able to make informed decisions,” Bauer said.

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This article originally appeared on USA TODAY: Tylenol during pregnancy: Researchers urge caution using acetaminophen