Acetaminophen use during pregnancy linked to language delays in children

The findings are reported in the journal Pediatric Research.

Earlier studies have found associations between acetaminophen use during pregnancy and poorer child communication skills. But those studies used measures of language development that were less precise than the methods applied in the current study, said Megan Woodbury, who led the research as a graduate student with U. of I. comparative biosciences professor emerita Susan Schantz. The work was conducted as part of the Illinois Kids Development Study, which explores how environmental exposures in pregnancy and childhood influence child development. Schantz is the IKIDS principal investigator. Woodbury is now a postdoctoral researcher at Northeastern University in Boston.

"The previous studies had only asked pregnant people at most once a trimester about their acetaminophen use," Woodbury said. "But with IKIDS, 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."

The language analyses involved 298 2-year-old children who had been followed prenatally, 254 of whom returned for further study at age 3.

For the 2-year-olds, the researchers turned to the MacArthur-Bates Communicative Development Inventories, which asks a parent to report on the child's vocabulary, language complexity and the average length of the child's longest three utterances.

"We wanted to collect data at that age because it's the period called 'word explosion,' when kids are just adding words every day to their vocabulary," Schantz said.

The vocabulary measure asked parents to select words their child had used from a list of 680 words.

The parents assessed their child again at 3 years, comparing their language skills to those of their peers.

The analysis linked acetaminophen use in the second and third trimesters of pregnancy to modest but significant delays in early language development.

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

"At age three, greater acetaminophen use during the third trimester was related to parents ranking their kids as lower than their peers on their language abilities," Schantz said. "That outcome was seen primarily in male children."

The most dramatic finding was that each use of acetaminophen in the third trimester of pregnancy was associated with an almost two-word reduction in vocabulary in the 2-year-olds.

"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 said.

Fetal brain development occurs throughout pregnancy, but the second and third trimesters are especially critical times, Schantz said.

"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 endocannabinoid system, which is also very important for fetal development," Woodbury said.

The findings need to be tested in larger studies, the researchers said. Until then, people should not be afraid to take acetaminophen for fever or serious pain and discomfort during pregnancy. Conditions like a very high fever can be dangerous and using a drug like acetaminophen will likely help.

"There aren't other 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."

This work was supported by the Children's Environmental Health and Disease Prevention Research Center funded by the National Institute of Environmental Health Sciences and the U.S. Environmental Protection Agency and the National Institutes of Health Environmental Influences on Child Health Outcomes program.