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• Posted January 4, 2024

Could Mom's Acetaminophen Use in Pregnancy Lead to Language Delays in Kids?

Acetaminophen, best known as Tylenol in the United States, is a go-to pain med for millions.

However, a new study is raising doubts about its safe use by women who are pregnant.

The researchers found kids born to women who used acetaminophen while pregnant had delays in language development, compared to children born to women who didn't use the drug.

This isn't the first time such an association has been found -- prior studies had found similar links when it came to kids' communication skills.

However, the new study used measures of language acquisition that were more precise than those used in prior research. It also tracked women's acetaminophen use more closely, the researchers said.

"The previous studies had only asked pregnant people at most once a trimester about their acetaminophen use,"said lead researcher Megan Woodbury. But in the new study, "we talked to our participants every four to six weeks during pregnancy and then within 24 hours of the kid's birth, so we had six time points during pregnancy," she said.

Woodbury led the research while a graduate student at the University of Illinois, Urbana-Champaign. She's now a postdoctoral researcher at Northeastern University in Boston.

The findings were published recently in the journal Pediatric Research.

The research was part of the ongoing Illinois Kids Development Study, focused on environmental factors in pregnancy and childhood that might affect childhood development.

Nearly 300 kids were included in the latest research. Their fetal environment was assessed, and each child's development was then gauged at ages 2 and 3.

Age 2 is a period of what senior study author Susan Schantz, a comparative biosciences professor emerita at the University of Illinois, called "word explosion," when new words get added to a child's vocabulary daily.

When kids reached this age, the Illinois team used a standard 680-word test of vocabulary to see how far along a child had progressed in terms of language. Children were then reassessed for language skills at age 3.

"We found that increased use of acetaminophen -- especially during the third trimester [of pregnancy] -- was associated with smaller vocabulary scores and shorter 'mean length of utterance' at two years,"Woodbury said in a Illinois news release.

There seemed to be a dose-response relationship: The more often a mom-to-be took acetaminophen in her third trimester, the bigger the language delay.

"This suggests that if a pregnant person took acetaminophen 13 times -- or once per week -- during the third trimester of that pregnancy, their child might express 26 fewer words at age 2 than other children that age,"Woodbury noted.

Schantz said that's in line with what scientists know about fetal brain development.

"Hearing is developing in the second trimester, but language development is already starting in the third trimester, before the baby is even born,"she said.

"It's thought that acetaminophen exerts its analgesic effect through the endo-cannabinoid system, which is also very important for fetal development,"Woodbury explained.

It's probably too early to tell women to stop taking acetaminophen during a pregnancy, and larger, more rigorous studies are needed to confirm these results, the researchers said.

Women who are pregnant often take a pain reliever to ease a high fever, for example, and leaving fevers untreated could bring its own risks to the fetus.

"There aren't other [treatment] options for people to take when they really need them,"Schantz said. "But perhaps people should use more caution when turning to the drug to treat minor aches and pains."

More information

Find out more about child language milestones at Stanford Medicine.

SOURCE: University of Illinois Urbana-Champaign, news release, Jan. 3, 2024