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Common medications used to treat rheumatoid arthritis may affect abortion rates in women, a new study suggests.

New research published in the journal Arthritis Care & Research reveals that women with rheumatoid arthritis (RA) taking methotrexate (MTX), a drug commonly used to treat inflammation caused by the autoimmune disease, had lower induced abortion rates compared to women with RA not taking the medication.

In contrast, women with RA taking anti-TNF drugs like Enbrel, Humira, and Remicade had higher abortion rates than women not exposed to the drugs.

Lead researcher Dr. Évelyne Vinet, from the Montreal General Hospital of the McGill University Health Center (MUHC) in Canada, looked the induced abortion rates in women with RA exposed to MTX using Quebec's physician billing hospitalization databases from 1996 to 2008.  They identified women with RA who were between the ages of 15 and 45, with cases classified as women who had an induced abortion. The study defined MTX exposure as filling a prescription for the drug less than 16 weeks prior to the date of abortion.

Researchers identified 112 women with RA who had an induced abortion and 5855 RA controls. Vinet and her team found that nearly 11 percent of women with RA who had induced abortions and 22 percent of controls were exposed to MTX.

The findings revealed that women with RA who were exposed to MTX had a lower rate of induced abortions compared to unexposed controls.  Furthermore, the findings showed a potential increase in the rate of induced abortions among women exposed to anti-TNF drugs like Enbrel, Humira and Remicade.

"Our study shows that women with RA who were on MTX had lower rates of induced abortions, while those exposed to anti-TNF medications had potentially higher abortion rates" Vinet said in a journal release.

"These findings highlight the importance of research on reducing the number of unplanned pregnancies in women with RA taking MTX or TNF inhibitors. Further examination of counseling practices and contraceptive use is warranted to further reduce the need for abortions in women with RA," she added.

An estimated 1.3 million adults in the U.S. have RA, an inflammatory disease where the immune system mistakenly attacks tissues in the joints causing pain, swelling, stiffness and potential loss of joint function.  RA affects women more than men, with the number of women with the condition outnumbering men by about three to one.

The condition can strike women during their reproductive years and place them at risk for unplanned pregnancies.  Previous research reveals that up to half of pregnancies in North American are unplanned and nearly half of these unintended pregnancies are aborted.

A 2003 study found that while 96 percent of U.S. rheumatologists had recommended birth control to female RA patients of childbearing age who were starting MTX, only 55 percent followed-up with patients regarding their use of contraceptives.

"Women with RA who become pregnant may have disease-specific reasons which might influence their decision to end a pregnancy," Vinet explained. "Exposure to teratogenic drugs, such as MTX, which can affect the development of the fetus, is one such reason women with RA may choose an induced abortion," she added.

Previous studies found that women with RA have higher risks of preeclampsia, preterm delivery, having underweight babies and needing a cesarean section, according to Reuters.