Myocardial Infarction and Past Oral Contraceptive Use

BACKGROUND: In the mid 1980s, it was known that current oral contraceptive use (in the preceding month) increased the risk of myocardial infarction three to four-fold. Evidence seemed to indicate that past use lasting a total of five or more years was associated with a residual two-fold increase in myocardial infarction risk among women 40 to 49 years old. Since the incidence of the disease started to become appreciable beyond age 49, it was of public health importance to reexamine the evidence in a data base which included women aged 50 or older to determine how long the increased risk persisted and whether it varied according to the formulation of the preparation used. An increase in risk that persisted after discontinuation of oral contraceptive use would have major public health implications since millions of women have used or will use oral contraceptives for long periods. DESIGN NARRATIVE: The design was that of a case-control study. Cases were identified by weekly telephone calls to the coronary care units of 78 hospitals in greater Boston, Southern Connecticut, and Westchester County. Nurse-interviewers administered standard interviews to cases convalescing on medical wards after discharge from coronary care units and to controls identified in the same hospitals. Histories of oral contraceptive use, including the timing and duration of use and the name of the preparations, were recorded along with information on other drug use and myocardial infarction risk factors such as cigarette smoking. Data were collected for three years. The study completion date listed in this record was obtained from the "End Date" entered in the Protocol Registration and Results System (PRS) record.