Some Common Painkillers Linked to Miscarriage Risk

Sept. 6, 2011 -- The use of certain non-aspirin anti-inflammatory painkillers during pregnancy may be associated with an increased risk of miscarriage, a large new study shows.

The study included more than 52,000 pregnant women in Canada. It found that miscarriage rates were more than twice as high among those who filled at least one prescription for a nonsteroidal anti-inflammatory drug (NSAID) compared to women who didn't get prescriptions for those kinds of medications.

NSAIDs include popular pain relievers like ibuprofen and naproxen. They are typically used to treat muscle injuries, headaches, and menstrual cramps.

Because they're so common, researchers say many women reach for them before they suspect they're pregnant.

"In our study, women used NSAIDs, on average, for four days during early pregnancy. That was enough to trigger an increased risk," says study researcher Anick Bérard, PhD.  Bérard is an epidemiologist and professor of pharmacy at the University of Montreal.

"Many of the drugs that are available over the counter are believed to be safe during pregnancy, which is not always the case. NSAIDs are a good example of that," she says.

The study is published in the Canadian Medical Association Journal.

A similar, large study by Danish researchers, published in BMJ in 2001, found that NSAID use was associated with a nearly threefold higher risk of miscarriage. But such studies can only show associations. They do not prove that NSAIDs cause miscarriages.

And experts say they often have weaknesses that make the links they find less reliable.

Miscarriages and NSAIDs

For the current study, researchers identified more than 4,700 women in Canada who had lost a baby before the 20th week of pregnancy.

Each one of those women was compared to 10 other women in a national registry of the same age who had not miscarried by the same point in her pregnancy.

Overall, 352 women (7.5%) of those who had miscarried had filled one or more prescriptions for an NSAID during pregnancy.

That compares with NSAID use in 1,213 women (2.6%) of those who had not miscarried.

The risk varied slightly by medication.

Women with prescriptions for diclofenac, for example, had about three times the risk of miscarriage compared to those who didn't take that medication. Those taking naproxen had a 2.64 times higher risk.

Celebrex and ibuprofen were each associated with a slightly more than doubled risk. Those taking Vioxx, which is no longer sold in the U.S., had an 83% greater risk.

Those risks remained when researchers adjusted their results to remove the influence of other things known to increase miscarriage risk, including a history of miscarriage and underlying health conditions like diabetes, depression, rheumatoid arthritis, lupus, and untreated thyroid disease.

The dose of the medication didn't seem to be tied to the degree of risk.

"This leads me to believe that women using NSAIDs over the counter, which are known to be lower dosage, are at the same risk as those who are going and getting a prescription," Bérard says.