Background: Low-dose oral contraceptives are widely used, but there are limited data on the cerebrovascular risks associated with these medications.
Objective: To determine whether use of low-dose oral contraceptives influences the risk for stroke.
Design: Population-based case-control study.
Setting: Women 18-44 years of age who resided in western Washington State between 1991 and 1995.
Participants: Patients with ischemic stroke (n = 60), hemorrhagic stroke (n = 102), and other types of stroke (n = 11) and controls identified through random-digit dialing (n = 485).
Measurements: Details about oral contraceptive use and other risk factors for stroke were obtained through in-person interviews.
Results: The estimated incidences of hemorrhagic stroke and ischemic stroke were 6.4 and 4.3 per 100,000 women-years, respectively. Compared with women who had never used oral contraceptives (after adjustment for risk factors for stroke), current users of low-dose oral contraceptives had estimated odds ratios of 0.93 (95% CI, 0.37 to 2.31) for hemorrhagic stroke and 0.89 (CI, 0.27 to 2.94) for ischemic stroke. Compared with past users of oral contraceptives, current users had odds ratios of 1.41 (CI, 0.67 to 2.96) for hemorrhagic stroke and 1.37 (CI, 0.49 to 3.81) for ischemic stroke. For past users compared with never users, the odds ratios were 0.59 (CI, 0.30 to 1.18) for hemorrhagic stroke and 0.57 (CI, 0.25 to 1.32) for ischemic stroke. The odds ratio for hemorrhagic stroke in current users of low-dose oral contraceptives containing norgestrel or levonorgestrel was elevated (3.23 [CI, 1.24 to 8.41]). Among patients with hemorrhagic stroke, the odds ratio for aneurysmal bleeding associated with current use of low-dose oral contraceptives containing norgestrel or levonorgestrel was 4.46 (CI, 1.58 to 12.53).
Conclusion: The overall risk for stroke and type of stroke was not increased among current users of low-dose oral contraceptives in the study population. Larger studies are needed to clarify both the relation of risk for stroke to past use of oral contraceptives and the possible association between current use of norgestrel-containing oral contraceptives and hemorrhagic stroke.
PIP: A case-control study of women 18-44 years of age residing in western Washington state (US) in 1991-95 failed to document an increased risk of stroke among users of low-dose oral contraceptives (OCs). Random digit dialing identified 60 cases of ischemic stroke, 102 cases of hemorrhagic stroke, and 11 other types of stroke; an additional 485 age-matched women were selected as controls. The estimated incidences of hemorrhagic stroke and ischemic stroke were 6.4 and 4.3 per 100,000 woman-years, respectively. Compared with women who had never used OCs (and after adjustment for stroke risk factors), current users of low-dose OCs had odds ratios of 0.93 (95% confidence interval (CI), 0.37-2.31) for hemorrhagic stroke and 0.89 (95% CI, 0.27-2.94) for ischemic stroke. Compared with past users of OCs, current users had odds ratios of 1.41 (95% CI, 0.67-2.96) for hemorrhagic stroke and 1.37 (95% CI, 0.49-3.81) for ischemic stroke. For past users compared with never users, the odds ratios were 0.59 (95% CI, 0.30-1.18) for hemorrhagic stroke and 0.57 (95% CI, 0.25-1.32) for ischemic stroke. The odds ratio for hemorrhagic stroke in current users of low-dose OCs containing the progestins norgestrel or levonorgestrel was 3.23 (95% CI, 1.24-8.41). Finally, among women with hemorrhagic stroke, the odds ratio for aneurysmal bleeding associated with current use of low-dose OCs containing norgestrel or levonorgestrel was 4.46 (95% CI, 1.58-12.53). These findings are consistent with those of other recent studies indicating that reductions in the estrogen content of OCs have greatly enhanced the cerebrovascular safety of these formulations. The slightly elevated risk of hemorrhagic stroke among users of OCs containing norgestrel requires further investigation.