Giant cell arteritis and polymyalgia rheumatica: are pregnancies a protective factor? A prospective, multicentre case-control study. GRACG (Groupe de Recherche sur l'Artérite à Cellules Géantes).

Objective, To assess the potential role of allo-immunization, either by former pregnancies, or by a history of blood transfusion, in the pathogenesis of giant cell arteritis and polymyalgia rheumatica. Methods. Two hundred and eighty-five incident female cases and 186 age-matched, population-based female controls were prospectively included in a multicentre case-control study. Results. The number of pregnancies was significantly lower in cases than in controls (nulliparous: 21.55% vs 12.90%; ≥4 pregnancies: 16.25% vs 27.42%; Wilcoxon rank sum test: P = 0.0019) in biopsy-proven or negative temporal arteritis and, to a lesser extent, in polymyalgia rheumatica. No difference was found for history of blood transfusion. Pregnancies remained negatively associated with the disease in a multivariate analysis including cardiovascular risk factors such as smoking or a pre-existing peripheral vascular disease. Conclusion. Former pregnancies are not a risk factor for giant cell arteritis. Pregnancies may be protective thanks to an effect of the associated hyperoestrogenic state against alterations of the artery wall, as suggested in animal models.