Fetal Cells May Lower Moms' Risk for Rheumatoid Arthritis

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Many moms-to-be experience back pain and achy joints during pregnancy. But in the long run, according to a new University of Washington study, pregnancy may actually work to reduce a woman's chances for developing rheumatoid arthritis (RA), a condition in which the immune system mistakenly attacks tissue in the joints, leading to inflammation, pain, and progressive joint damage.

Published March 22, 2010, in the online edition of the journal Arthritis & Rheumatism, researchers examined the pregnancy histories of 310 women who had been newly diagnosed with RA and 1,418 women without the disease. In their findings, researchers noted that women who had had at least one child were 39 percent less likely to have RA than women who had never been pregnant—even with age and other factors linked to a lower RA risk (i.e., oral contraceptive use), taken into account.

What seemed to matter most in determining a mom's risk for RA was the amount of time that had elapsed since her last pregnancy. According to a Reuters Health story on the study, women who had had their last child within the past five years were 71 percent less likely than childless women of the same age to have RA; women who had last given birth more than 15 years ago were 24 percent less likely than same-age counterparts to be diagnosed with the condition.

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What's the connection? Researchers speculate that fetal cells—leftover cells from a baby that remain circulating in a mother's bloodstream for years after giving birth—have some sort of protective effect against certain diseases, including rheumatoid arthritis.

"The most exciting result for us was the relationship of a woman's risk for developing RA with time from childbirth—in particular diminishing protection over time—because this observation supports our hypothesis that fetal cells, now known to persist for decades after a birth, may benefit the mother," says study lead author Dr. Katherine A. Guthrie, in an interview with Reuters Health. Other research has found that leftover fetal cells may promote cell repair in moms (acting much like stem cells), potentially lowering a mom's risk for certain cancers and other autoimmune diseases.