Parity status and the development of rheumatoid arthritis.

Rheumatoid arthritis (RA) is one of a number of autoimmune diseases with a marked female excess in incidence, particularly during the reproductive years. It is of interest to investigate whether reproductive factors are important in determining susceptibility to RA. However, difficulties in dating the pathological onset of the disease can make it difficult to distinguish between the reproductive influence history on disease and the influence of (subclinical) disease on reproduction. In women with RA compared to controls, there is no excess of being unmarried. Most but not all studies, show an increase in nulliparity, whereas parity rates in fertile RA women are unchanged. There is an increased rate of onset postpartum, particularly in the first three months after delivery. There is no unifying biological explanation for these epidemiological findings, and it is likely that the apparently obvious link between reproductive experience and pregnancy is complex.