An examination of the role of female hormones and pregnancy as risk factors for rheumatoid arthritis, using a male population as control group.

While being female is known to increase the risk of developing rheumatoid arthritis approximately threefold, this study, by making use of a male control group, suggests that female sex hormones per se are unlikely to be the main cause of this discrepancy. Apart from the teens, when rheumatoid disease is extremely rare in males, the female/male incidence ratio remains almost constant throughout the adult age range, in spite of the reduction in endogenous oestrogen levels at the menopause. Pregnancy is known to ameliorate RA, but this study found that it was also the most common identifiable event preceding the onset of RA in women of childbearing age (22%), which may explain the apparent protective role of oral contraceptives in this age group.