Dear Doctor: Will taking acetaminophen (Tylenol) during pregnancy increase the chances that the child will have ADHD or autism?

Dear Reader: Such concern is understandable. Parents and parents-to-be have been alarmed over the past few years by two Danish studies that raise the specter of greater ADHD and autism risks among children whose mothers took the over-the-counter pain killer acetaminophen during pregnancy. But let’s look at these studies a little more closely.

The largest of these studies showed that, among children whose mothers ever used acetaminophen during pregnancy, 5.7 percent showed symptoms of hyperactivity by age 7. Among children whose mothers never took acetaminophen, 4.3 percent showed symptoms of hyperactivity. Similar mild differences were also noted for emotional problems and overall conduct.

Here’s the important caveat: The two groups of women were themselves very different. Participants who used acetaminophen were more likely to be smokers, more likely to be obese (BMI greater than 30) and more likely to have had a fever. Just having a fever during pregnancy has been associated with autism, behavioral abnormalities and problems with attention.

As for the autism study, it linked acetaminophen use during pregnancy to an IQ drop of 2 points in 5-year-olds. Here, the cause of the acetaminophen use is an especially important factor. In this study, 37 percent of the mothers who used acetaminophen had fever; only 23 percent of those who didn’t use acetaminophen had fever. And again, those who used acetaminophen were more likely to be smokers.

So one has to ask: Why does someone take acetaminophen during pregnancy? The answer: To reduce a fever. So fever may be the problem, not the acetaminophen. Further, women who smoke and are obese are more likely to be unhealthy during pregnancy, more likely to take acetaminophen for physical problems and more likely to have children who may also be less healthy.

Would I recommend acetaminophen regularly in pregnancy for joint pain and muscle aches? Probably not, though I would take it for a fever and for moderate pain. Otherwise, it’s better to do prenatal yoga, gentle stretching and maintain a good diet.

Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.