Background: The overprevalence of giant cell arteritis (GCA) and polymyalgia rheumatica (PMR) in women remains unexplained. Microchimerism pathogenicity has been discussed in some systemic diseases. We tested history of pregnancy as a risk factor for GCA.
Methods: Prospective, multicenter case-control study with multiple, age-matched, control groups. Patients have been included in 40 different centers. The first control group has been randomly selected in the general population, consecutive hospitalized patients in two geographically distant departments of internal medicine made up the second and third ones.
Results: Three hundred and fifteen patients (249 GCA and 66 PMR), 242 general population controls, 333 in the first hospitalized control group, and 355 in the second, have been included in the 1991-1998 period. Pregnancy has been constantly protective against GCA/PMR (Wilcoxon rank sum test: P = 0.0001, 0.0005, and 0.054, respectively, for the three control groups), more particularly for parity equal or greater than 4 (OR = 0.32, 95% CI: 0.18-0.57, P = 0.00003; OR = 0.44, 95% CI: 0.26-0.74; P = 0.0009, and OR = 0.42; 95% CI: 0.25-0.71, P = 0.0006, respectively). In multivariate analysis, risk for GCA on pre-existing degenerative, vascular disease is decreased by half for each pregnancy (OR = 0.49, 95% CI = 0.27-0.90, P = 0.022).
Conclusion: Contrary to the initial hypothesis, multiparity is a protective factor against GCA. Mechanism is unknown.