Oral contraceptives and rheumatoid arthritis: results from a primary care-based incident case-control study.

ObjectiveThe possibility that oral contraceptives offer a protective effect against the development of rheumatoid arthritis is still contentious. Of the 17 studies investigating this association, 11 have found a protective effect, and 6 have not. These differences are probably attributable to either selection or information biases in a subset of studies, although the exact reason is unknown. To overcome the methodological problems inherent in the design of previous studies, we have conducted a population-based case-control study.MethodsWomen who were incident cases of inflammatory polyarthritis, defined as swelling of at least two joint areas lasting at least 4 weeks, were recruited directly from primary care and compared with age-matched women from the same population.ResultsCases and controls reported a similar level of "ever use" of oral contraceptives, adjusted odds ratio = 0.88 (95% confidence interval, 0.47, 1.64). The cases were, however, less likely to report using oral contraceptives at the time of onset, adjusted odds ratio = 0.22 (95% confidence interval, 0.06, 0.85). Similar results were observed for cases who satisfied the criteria for rheumatoid arthritis and cases who did not.ConclusionThese results indicate that only current oral contraceptive use protects against the development of inflammatory polyarthritis.