Hormonal factors and risk of aneurysmal subarachnoid hemorrhage - An international population-based, case-control study

Background and Purpose-Subarachnoid hemorrhage (SAH) is more common in wome n than in men, but the role of hormonal factors in its etiology remains unc ertain. The aim of this study was to examine the relationship between hormo nal factors and risk of SAH in women. Methods-This was a prospective, multicenter, population-based, case-control study performed in 4 major urban centers in Australia and New Zealand. Two hundred sixty-eight female cases of first-ever aneurysmal SAH occurred dur ing 1995-1998. Controls were 286 frequency-matched women from the general p opulation of each center. Outcome measures included risk of SAH associated with use of oral contraceptive pills (OCPs), hormone replacement therapy (H RT), and various endogenous hormonal factors including menstrual patterns, parity, age at birth of first child, and breast-feeding practices. Results-Cases and controls did not differ with regard to menstrual and repr oductive history except in age at bir th of first child, where older age wa s associated with reduced risk of SAH (odds ratio [OR], 0.63; 95% CI, 0.43, 0.91). Relative to never use of HRT, the adjusted OR for over use of HRT w as 0.64 (95% CI, 0.41, 0.98), which did not alter significantly after furth er adjustment for possible confounding factors. Borderline evidence of an i nverse association was detected for past use of HRT (adjusted OR, 0.59; 95% CI, 0.30, 1.13) and current use of HRT (adjusted OR, 0.67; 95% CI, 0.40, 1 .13), but there was no evidence of an association for use of OCPs (adjusted OR, 0.97; 95% CI, 0.58, 1.60). Conclusions-The risks of SAH are lower in women whose first pregnancy is at an older age and women who have ever used HRT but not OCPs. The findings s uggest an independent etiologic role for hormonal factors in the pathogenes is of aneurysmal SAH and provide support for a protective role fur HRT on r isk of SAH in postmenopausal women.