The activity of RA is significantly altered by pregnancy with approximately 70 per cent of patients experiencing substantial improvement in symptoms, signs and sometimes extra-articular manifestations. This lessening of disease activity occurs in association with an almost complete cessation of medications. However, whether partial or complete this remission is short-lived with more than 90 per cent of women who improved relapsing by 6 to 8 months postpartum. Further, in approximately 30 per cent of RA patients the course remains unchanged or worsens during gestation and indeed the first symptoms of RA may develop during pregnancy or shortly thereafter. Conversely active rheumatoid arthritis seems to little influence the maternal course or fetal outcome of pregnancy. The multiple and complex immunologic alterations of the pregnant state are designed to ensure survival of the fetal allograft in a foreign host. A number of these alterations particularly involving modulation of cell-mediated immunity, immunoglobulin composition, immune complex generation, or the inflammatory response have the potential to interfere with the pathophysiology of RA. In short, although the specific mechanism remains an enigma, the reason for the amelioration of RA during pregnancy is probably an incidental and fortuitous reaction to one or more of these immunomodulatory factors.