Investigation of Relation between Use of Oral Contraceptives and Thromboembolic Disease. A Further Report

Abstract

The results of a previous study of the use of oral contraceptives by married women discharged from hospital with a diagnosis of thromboembolic disease in the years 1964–6 were reported by us last year. The present paper adds results relating to patients discharged during 1967 and a few data, that could not be sought previously, for patients discharged with cerebral or coronary thrombosis from three of the hospitals in the earlier period. Of 84 patients with deep-vein thrombosis or pulmonary embolism 42 (50%) had used oral contraceptives during the month preceding the onset of their illness, while only 23 of the 168 controls (14%) had done so. No differences in risk were found either for the types of preparation or for the duration of use. After allowance for age and height, the patients with venous thromboembolism were about 10 lb. (4,535 g.) heavier than the control patients, irrespective of whether they were using oral contraceptives or not. No appreciable difference was found between the smoking habits of patients with and without venous thromboembolism treated during 1967, nor between women who were using oral contraceptives and those who were not. The trend in hospital admissions for venous thromboembolism with time corresponded to the trend in the use of oral contraceptives, and there was no evidence to suggest that the number of admissions was affected by publicity about the risk of using the preparations. Of 19 patients with cerebral thrombosis 11 (58%) had been using oral contraceptives, compared with an expected figure of 3.5 from the experience of the control subjects. All the published data (clinical, angiographic, and post-mortem) show that the thrombosis affects the cerebral arteries rather than the cerebral veins. Of 17 patients with coronary thrombosis 2 (12%) had been using oral contraceptives, compared with an expected figure of 2.1. The patients with coronary thrombosis smoked more than the control patients and were, on average, 8.3 lb. (3,765 g.) heavier than control women of the same age and height. The new evidence strengthens the belief that oral contraceptives are a cause of venous thromboembolism and cerebral thrombosis but does not indicate that they are a cause of coronary thrombosis.