BACKGROUND:

Post-menopausal women who use estrogens generally experience at once a reduced risk of coronary heart disease and, at the same time, an increased risk of endometrial cancer. In order to protect the endometrium from unopposed estrogens, many physicians now recommend the addition of a progestin during 10-13 days of the cycle. Progestins may be implicated in the increased risk of myocardial infarction in women on oral contraceptives.

DESIGN NARRATIVE:

This was a case-control study. The computerized files of the Group Health Cooperative (GHC) in Seattle were used to identify cases. All postmenopausal women, aged 40 to 79, were eligible as cases if, according to World Health Organization criteria, they presented with a fatal or non-fatal myocardial infarction. A random sample of women listed in the enrollment files at GHC served as a source of potential controls. Review of the out-patient medical records, performed by an assistant blind to case-control status ensured that all study subjects met the same criteria. Telephone interviews were used to obtain information about exposure to postmenopausal hormones as well as known risk factors. The computerized pharmacy records at GHC provided additional information about exposure. Frequency matching controlled for the potential confounding effects of age and year of presentation.

Stratification and logistic regression were used in data analysis.

The study was renewed in 1995 to make more precise some of the indeterminate findings related to current use, cumulative dose and duration of use but also to extend the assessment of the risk or benefit to incident strokes. The study ended in January, 1999.