New Study Links Tylenol Use During Pregnancy to a Delay That's Only Found in Girls

Before you take a Tylenol to help soothe that pregnancy headache, you might want to read the latest findings on what delays acetaminophen — the active ingredient found in many over-the-counter pain and fever relievers — might cause in babies . . . particularly baby girls.

In the first study of its kind, published in the European Psychiatry's journal last month, researchers have found an elevated rate of language delay in girls born to mothers who used acetaminophen during pregnancy, but not in boys.

Nearly 800 pregnant Swedish women took part in the study, which used self-reporting and urine samples to determine acetaminophen concentration. The researchers then compared this data with not only the mothers' assessments of their now two-and-half-year-old children's developmental milestones, but also with the scores on a language-based screening that was given to all children in Sweden at 30 months.

Here's what they discovered: 59 percent of the women studied used acetaminophen, and 10 percent of the children in the study had a language delay, with greater delays in girls versus boys.

"It's important for us to look at language development because it has shown to be predictive of other neurodevelopmental problems in children," said the study's senior author, Dr. Shanna Swan, a professor at the Icahn School of Medicine at Mount Sinai.

What was most telling, however, was that girls born to mothers with a higher exposure to acetaminophen — which they defined as taking the medication more than six times in early pregnancy — were nearly six times more likely to have a language delay than girls whose mothers didn't take the drug.

This difference simply wasn't demonstrated with mothers of boys. In fact, women with high concentrations of acetaminophen appeared slightly less likely to have language-delayed sons.

It's unclear why drugs like Tylenol affect boys and girls differently, but the researchers find it interesting that the results work against the "well-recognized female advantage" that girls tend to have over boys in factors like expressive speech and vocabulary.

And although they stress that the findings can only pinpoint associations, not cause and effect, Dr. Swan has a clear recommendation:

"Given the prevalence of prenatal acetaminophen use and the importance of language development, our findings, if replicated, suggest that pregnant women should limit their use of this analgesic during pregnancy."