Women with rheumatoid arthritis may have a somewhat harder time becoming pregnant, a new study suggests.
The study, of more than 68,000 pregnant women, showed that those with rheumatoid arthritis generally had a tougher time conceiving compared to women without the disease.
The researchers found that 25 percent of women with rheumatoid arthritis had tried unsuccessfully for at least a year before they finally became pregnant, whereas only 16 percent of women without the disease had needed that much time. And 10 percent of the women with RA had been treated for infertility, compared with just under 8 percent of other women.
Rheumatoid arthritis (RA) arises when the immune system mistakenly attacks tissue in the joints, leading to inflammation, pain and progressive joint damage. The disease is more common in women than men, and though it most often arises in middle-age, it can affect young adults too.
RA is not the same as the more familiar osteoarthritis, which commonly affects elderly people and athletes and is caused by wear and tear on the joints.
It has not been clear whether RA, or the drugs used to treat it, might interfere with a woman's fertility.
This latest study, published in the journal Arthritis & Rheumatism, does not definitively answer that question. It's possible that other factors might explain the longer time to pregnancy among women with RA.
"We do not know whether the longer time to pregnancy is caused specifically by RA or its treatment," said lead researcher Dr. Damini Jawaheer, of Children's Hospital Oakland Research Institute in Oakland, California.
In an e-mail to Reuters Health, Jawaheer said there is no evidence that the disease or its medications affect a woman's ability to conceive. "But on the other hand," she said, "little is known about the effects of RA treatment in this context."
Jawaheer pointed out that women who are trying to become pregnant are often told to stop using RA medications known as disease-modifying anti-rheumatic drugs (DMARDs), like methotrexate (Rheumatrex), etanercept (Enbrel) and infliximab (Remicade).
That's because some, like methotrexate, can cause birth defects. With newer DMARDs, like etanercept and infliximab, there is not yet enough evidence to know whether they are safe during pregnancy.
It's possible, Jawaheer speculated, that when women stop taking their medication, there is a flare-up of the RA that somehow hinders their ability to conceive.
"However," she said, "additional work is needed to investigate this and other potential causes further."
The findings are based on 68,170 Danish women who became pregnant between 1996 and 2002. Of those women, 112 had been diagnosed with RA before pregnancy.
In general, the women with RA took longer to conceive. They were also somewhat less likely to become pregnant within 2 months of trying -- 41 percent did, versus 48 percent of women without RA.
When the researchers took other factors into account, like age and body weight, women with RA were 60 percent more likely than the other women to need more than a year to conceive.
But while that figure sounds large, it suggests that for any one woman with RA, the odds of a delayed pregnancy would be only "slightly" increased, according to Jawaheer.
That said, she added, "it may be a good idea for young women with RA not to delay their plans to conceive until the late reproductive years."
Most women with RA, Jawaheer said, are ultimately able to conceive.