Ischemic stroke risk with oral contraceptives - A meta-analysis

Context The relationship between ischemic stroke and oral contraceptive (OC ) use has been studied for 40 years, but disagreement about an association persists. Objective To review available literature to determine whether OC use is ass ociated with increased stroke risk. Data Sources Studies published from January 1960 through November 1999 were identified from electronic databases (MEDLINE, BIOSIS, and Dissertation Ab stracts Online), Index Medicus, bibliographies of pertinent review articles and pertinent original articles, textbooks, and expert consultation, Study selection From 804 potentially relevant references retrieved, 73 were studies investigating risk of ischemic stroke with OC use. Two reviewers i ndependently applied the following inclusion criteria: more than 10 stroke cases sampled, clear stroke subtype differentiation, concurrent controls in cluded, adequate data included to determine relative risks (RRs) and confid ence intervals (Cls), analysis controlled Cor age, and no later publication of identical data. A third investigator adjudicated disagreements. Sixteen studies met all inclusion criteria and were included in the meta-analysis. Data Extraction Two investigators independently extracted data, with disagr eements resolved through discussion. Data Synthesis The 16 studies were analyzed using random effects modeling. Current OC use was associated with increased risk of ischemic stroke (RR, 2 .75; 95% CI, 2.24-3.38). Smaller estrogen dosages were associated with lowe r risk (P = .01 for trend), but risk was significantly elevated for all dos ages, Studies that did not control for smoking (P = .01) and those using ho spital-based controls (P < .001) found higher RRs, but no other patient cha racteristics or elements of study design were important. The summary RR was 1.93 (95% CI, 1.35-2.74) for low-estrogen preparations in population-based studies that controlled for smoking and hypertension. This translates to a n additional 4.1 ischemic strokes per 100000 nonsmoking, normotensive women using low-estrogen OCs, or 1 additional ischemic stroke per year per 24000 such women. The RR of stroke due to OC use was not different in women who smoked, had migraines, or had hypertension. Conclusions Summary results indicate that risk of ischemic stroke is increa sed in current OC users. even with newer low-estrogen preparations. However , the absolute increase in stroke risk is expected to be small since incide nce is very low in this population.