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

OBJECTIVE: The 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. METHODS: Women 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. RESULTS: Cases 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. CONCLUSION: These results indicate that only current oral contraceptive use protects against the development of inflammatory polyarthritis.