Women who take over-the-counter painkillers during early pregnancy have a slightly higher risk of having babies with certain rare birth defects, according to a new study.
For instance, babies were three times as likely to be born with no eyes, or with abnormally small eyeballs that often cause blindness, if their mothers had taken aspirin or naproxen (sold as Aleve).
The babies' risk of amniotic band syndrome, a condition that causes various malformations such as clubfoot, was also three times higher among women who had used painkillers during their pregnancy.
It is not clear that the painkillers caused the deformities, however. And even if they did, the risks are minute.
"These are pretty rare birth defects, so the effect is small," said Dr. Eva Pressman, who studies maternal-fetal medicine at the University of Rochester Medical Center but was not involved in the new work.
"A two-fold increase is still rare in the big picture," she told Reuters Health.
According to the Centers for Disease Control and Prevention, these eye defects, called anophthalmia and microphthalmia, occur in one out of 5,300 births in the U.S. About one out of 10,000 babies are born with amniotic band syndrome.
The new findings, published in the American Journal of Obstetrics and Gynecology, are based on data from the National Birth Defects Prevention study.
In that study, women from across the U.S. were interviewed about the drugs they took during the first trimester of their pregnancy. For example, they were asked whether they used common painkillers -- also known as nonsteroidal anti-inflammatory drugs or NSAIDs -- including aspirin, naproxen and ibuprofen (sold as Advil).
Researchers then compared the use of painkillers among 15,000 women whose babies had birth defects and 5,500 women whose babies were born without any deformities.
"Of the 29 different defects we examined, we were happy that a vast majority were not tied to NSAIDs," said study co-author Martha Werler, who studies birth defects at Boston University.
However, a few different types of birth defects were slightly increased in babies whose mothers reported taking ibuprofen, aspirin or naproxen.
For instance, the risk of cleft palate rose by 30 to 80 percent. And the risk of spina bifida, in which the spinal cord doesn't develop properly, jumped by 60 percent in babies whose mothers had used aspirin or ibuprofen.
While the results don't prove that painkillers are to blame, Werler said, they are a warning sign and warrant further research.
"Until we know more information, women should consult with their doctor to weigh risks and benefits of taking pain medication," Werler told Reuters Health.
Pressman said women who've taken NSAIDs during the first trimester of their pregnancy shouldn't worry. But to play it safe, she recommends avoiding that specific class of drugs while pregnant.
"For pain I recommend taking Tylenol, which works through a different mechanism of action, and is considered safe for pregnancy," she told Reuters Health.