Objective: To systematically review the literature on female risk factors and risk of SAH.
Methods: We searched Medline and EMBASE for articles published between January 1985 and July 2011. For all studies fulfilling the predefined criteria, we obtained risk ratios (RRs) or odds ratios (ORs) with 95% confidence intervals (CIs) for female risk factors. We pooled crude and adjusted ORs (aORs) with a general variance-based random-effects method. We evaluated methodologic quality with the Newcastle-Ottawa Scale.
Results: We included 16 studies; 8 had good quality. Twelve studies had a case-control design, 3 studies had a longitudinal design, and 1 study had a case-crossover design. Overall aORs were 1.31 (95% CI 1.05-1.64; 5 studies, 2 with good quality [GQ]) for current use of combined oral contraceptives (COC), 0.90 (95% CI 0.74-1.09; 7 studies, 4 GQ) for ever COC use, 0.86 (95% CI 0.69-1.08; 6 studies, 3 GQ) for current use of hormone replacement therapy (HRT), 0.74 (95% CI 0.54-1.00; 3 studies, 1 GQ) for ever use of HRT, and 1.29 (95% CI 1.03-1.61; 5 studies, 2 GQ) for postmenopausal women. Data on parity and age at menarche were heterogeneous. Risk of subarachnoid hemorrhage (SAH) was not increased during pregnancy, labor, or puerperium (RR 0.40, 95% CI 0.20-0.90; 1 GQ study).
Conclusions: Female hormone levels might influence risk of SAH, but the pathophysiology of this effect and its influence on the difference in incidence of SAH between the sexes remains unclear. Further studies are needed to identify modifiable risk factors of SAH in women older than age 50.