title: The pill, parity, and rheumatoid arthritis.
abstract: We report on a case-control study investigating the relationship of oral contraceptive pill (OCP) use and parity to the development of rheumatoid arthritis (RA). Women with RA were compared with 2 separate control groups, women with osteoarthritis (OA) and women randomly selected from a population-based electoral register. Nulliparity was found to be a risk factor for the development of RA, with age-adjusted odds ratios of 1.82 (95% confidence interval [CI] 1.09-3.03) versus the OA control group and 1.83 (95% CI 1.03-3.06) versus the population control group. Use of OCPs before the age of 35 was negatively associated with RA (odds ratio 0.56, 95% CI 0.29-1.12 versus the OA control group; odds ratio 0.6, 95% CI 0.30-1.17 versus the population control group). Some evidence of a duration-response effect was seen, although the numbers were small. The 2 variables were also multiplicative, with nulliparous non-OCP users having a 4-fold risk of RA compared with parous OCP users. These findings suggest that pregnancy and OCP use have a "protective effect" on the development of RA, although the mechanism remains unclear.
authors.affiliation: Department of Epidemiology, London Hospital Medical College, United Kingdom.
authors.forename: T D
authors.initials: TD
authors.lastname: Spector
authors.forename: E
authors.initials: E
authors.lastname: Roman
authors.forename: A J
authors.initials: AJ
authors.lastname: Silman
mesh_terms: D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000453:epidemiology*; D016022:Case-Control Studies; D003276:Contraceptives, Oral; D005260:Female; D006801:Humans; D008875:Middle Aged; D010003:Osteoarthritis / Q000453:epidemiology; D010298:Parity
chemical_list: D003276:Contraceptives, Oral