JACKSONVILLE, Fla. -

Acetaminophen is the most commonly used medication for pain and fever during pregnancy. But a new study finds women who take it when pregnant may be exposing their unborn baby to an increased risk of behavioral problems, like attention deficit/hyperactivity disorder, and hyperkinetic disorders like Tourette syndrome.

"So, it really, you know, takes a medication that's generally considered to be safe during the use of pregnancy and is used extensively and paints a different picture- maybe there are some issues here," explained Cleveland Clinic Obstetrician Dr. Jeff Chapa, who did not take part in the study.

UCLA researchers studied more than 64,000 children and their mothers in the Danish National Birth Cohort from 1996 to 2002. More than half of the mothers reported using acetaminophen while pregnant.

Results show the use of acetaminophen during pregnancy appeared to be associated with a higher risk of hyperkinetic disorders, or of having adhd-like behaviors at age 7. Stronger associations were observed with use in more than one trimester during pregnancy.

Chapa says acetaminophen is known to affect the levels of some pregnancy and thyroid hormones, particularly in the fetus.

"We know that these hormones are important in the development of the nervous system, so that might be a plausible, biological explanation for how acetaminophen could increase the risk for these disorders," Chapa said.

Researchers say more studies are needed because the exposure and the outcomes are frequent. Chapa agrees and says this study alone should not steer women away from acetaminophen use.

"We're not saying not to take acetaminophen at all during pregnancy, but I am saying that we should be judicious and smart about it," said Chapa. "If you're taking it over and over for weeks, maybe there is something else you can do instead."

Complete findings for this study are in the journal JAMA Pediatrics.