Common Painkiller Use May Be Linked to Miscarriage Risk

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A new study from the University of Montreal suggests a possible link between the use of nonaspirin painkillers like ibuprofen (Advil) in early pregnancy and a higher risk of miscarriage.

The researchers looked at more than 52,000 pregnant women in Canada, and found that those who received at least one prescription for a nonsteroidal anti-inflammatory drug, or NSAID, in early pregnancy, were more than twice as likely to have a miscarriage than women who didn’t get a prescription.

NSAIDs include prescription drugs like diclofenac, celecoxib (Celebrex) and rofecoxib (Vioxx), a painkiller that is no longer sold in the U.S., as well as over-the-counter painkillers like ibuprofen (Advil) and naproxen (Aleve).

About 4,700 women included in the study had a miscarriage before the 20th week of pregnancy. The researchers compared each of those women to 10 others of the same age who had not miscarried by the same point in their pregnancies. Among women who miscarried, 7.5% (352 women) had filled at least one NSAID prescription, compared with 2.6% (1,213 women) who didn’t have a miscarriage.

The risk of miscarriage was independent of the dose of drug that women were prescribed, the study found. “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,” study author Anick BĂ©rard, a professor of pharmacy at the University of Montreal, told WebMD.

Previous research, including a large study by Danish researchers in 2001 and a smaller survey by researchers in California in 2003, has also reported potential links between NSAID use and higher risk of miscarriage.

But these studies can show only associations and cannot prove that using NSAIDs directly causes miscarriage. “The problem is that type of study does not prove anything, but they scare the hell out of women and health professionals,” Dr. Gideon Koren, director of the Motherisk program at Toronto’s Hospital for Sick Children, told CBC News.

Indeed, the current study has many limitations. Among them:

  • The researchers used NSAID prescriptions as a marker for actual painkiller use, but getting a prescription doesn’t necessarily mean patients take the drug. A recent Swedish study of pregnant women who received prescriptions for medication to treat migraine headaches found that many never took the drugs.
  • The painkiller ibuprofen is available over the counter in Canada (as it is in the U.S.), but since the study looked only at prescriptions, many women taking ibuprofen may not have been counted.
  • More women who had miscarriages had other illness in the year before pregnancy than women who did not miscarry. The miscarriage group also had higher rates of depression and anxiety and were more likely to be poor. (The researchers tried to account for the influence of these and other factors known to increase miscarriage risk, including a history of miscarriage and underlying health conditions like diabetes, rheumatoid arthritis and lupus.)

Further, the problem with studying miscarriage is that it often happens before women even know they’re pregnant, so it is tricky to pin down.

Despite the limitations of the current study, the authors suggested that women in early pregnancy who need pain relief for acute conditions, such as headache, opt for non-NSAID drugs like acetaminophen.

The research appeared in the Canadian Medical Association Journal on Tuesday.

Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.