SEATTLE, July 10 -- Circulating fetal cells may account for why rheumatoid arthritis tends to improve or even disappear during pregnancy, according to researchers here.
For every doubling of fetal DNA in a pregnant woman's bloodstream, the likelihood of her arthritis improving increased by 20%, said Zhen Yan, M.D., Ph.D., of the Fred Hutchinson Cancer Research Center, and colleagues, reported in the July issue of Arthritis & Rheumatism.
The study included 25 pregnant women. Of these, 19 had adult onset RA and six had juvenile idiopathic arthritis. Serum levels of fetal DNA were measured at least three times during the pregnancy and about three months after delivery. The women's disease status was assessed each trimester and three to four months after giving birth.
A large proportion of fetal cells in a pregnant woman's bloodstream come from placental cells that have died off as the placenta grows, the researchers noted.