MYOCARDIAL-INFARCTION IN USERS OF LOW-DOSE ORAL-CONTRACEPTIVES

Objective: To determine the relationship between the use of low-dose ( less than 50 mu g estrogen) oral contraceptives (OC) and myocardial in farction. Methods: In this population-based case-control study, all in cident myocardial infarctions in women, ages 15-44 years who were memb ers of the Kaiser Permanente Medical Care Program, Northern and Southe rn California regions were ascertained during a 39-month period from 1 991 through 1494. For each woman with myocardial infarction, up to thr ee age- and facility-matched controls were chosen at random from femal e members. Information about OC use (predominantly low-dose preparatio ns) was obtained in face-to-face interviews. Results: There were 187 i ncident cases of myocardial infarction during 3.6 million woman-years of observation (incidence rate, 5.2 per 100,000 woman-years). The prev alence of several risk factors for myocardial infarction was lower in controls who were current users of OCs than in controls who were noncu rrent (past and never) users. The adds ratio for myocardial infarction in current OC users compared with noncurrent users was 1.65 (95% conf idence interval 0.45, 6.06) after adjustment for major risk factors an d for race and ethnicity, corresponding to an excess risk of less than one case per 100,000 woman-years. The study had 80% power to detect a relative risk of 2.3 (one-sided test, alpha = .05). The odds ratio of myocardial infarction in past OC users was not elevated. Conclusion: With respect to myocardial infarction, low-dose oral contraceptives ca n be used safely by women who lack risk factors for coronary heart dis ease. Copyright (C) 1996 by The American College of Obstetricians and Gynecologists. Copyright (C) 1996 by The American College of Obstetric ians and Gynecologists.