Investigation of Relation Between Use of Oral Contraceptives and Thromboembolic Disease

Abstract

Married women aged 16 to 40 years discharged during 1964–66 from 19 large general hospitals in the North-West Metropolitan Regional Hospital Board area with a diagnosis of deep vein thrombosis or pulmonary embolism without evident predisposing cause were identified by means of the hospital diagnostic indexes. They were subsequently interviewed in their homes, when inquiries were made about their past medical, obstetric, social, family, and contraceptive histories. For comparison, married control patients admitted to the same hospitals with acute surgical or medical conditions, or for elective surgery, and matched with the affected patients for age, parity, date of admission, and absence of any predisposing cause of thromboembolic disease, were also identified and similarly interviewed. Of 58 affected patients 26 (45%) had been using oral contraceptives during the month preceding the onset of their illness while only 10 of the corresponding 116 controls (9%) had been doing so. From these data it is calculated that the risk of hospital admission for venous thromboembolism is about nine times greater in women who use oral contraceptives than in those who do not. If national supply data are used for estimating the frequency of use of oral contraceptives in the general population it is calculated that about 1 in every 2,000 women using oral contraceptives are admitted to hospital each year with “ idiopathic ” venous thromboembolism in comparison with about 1 in every 20,000 women not using them. These results are not thought to have been produced by bias or by any common factor responsible both for the use of oral contraceptives and the production of thromboembolism, and it is concluded that oral contraceptives are a cause of the disease. At 16 hospitals women suffering from coronary or cerebral thrombosis were also studied. Five of nine patients who survived an attack of “ cerebral thrombosis ” had been using oral contraceptives during the month preceding their illness. Taken in conjunction with other similar findings, it is justifiable to conclude that oral contraceptives can also be a cause of cerebrovascular insufficiency. Of the 13 women who survived an attack of coronary thrombosis without evident predisposing cause none had been using oral contraceptives. © 1968, British Medical Journal Publishing Group. All rights reserved.