Effects of synthetic and natural estrogens on the coagulation system in post-menopausal women

Abstract

The effects of hormones on the blood clotting system can be studied in two different ways. The first involves detailed laboratory studies of hormones in small groups of women to define any consistent effects on the proteins concerned with blood coagulation. The second involves epidemiological studies in a large population to determine the incidence of thrombosis in women taking hormones compared with a matched population of women not using such therapy. The controlled studies carried out by the Royal College of General Practitioners in the United Kingdom and by Sartwell and his co-workers in the United States indicate that during the reproductive years the risk of developing deep vein thrombosis and pulmonary embolism is increased at least five-fold by the use of oral contraceptives¹. The epidemiological data on the thromboembolic complications associated with oral contraception did not become available until almost 15 years after the introduction of oral contraception. If, as seems likely, estrogen replacement therapy after the menopause is to be used on a scale as great as oral contraception, it is important that the effects of this therapy on the clotting system in post-menopausal women should be carefully investigated, as this may assist in the development of formulations which do not increase the risk of thrombosis. In this way, we may avoid exposing millions of women to the risk of thromboembolism. We have investigated three formulations of estrogen therapy, which are used in post-menopausal women to determine their effects on certain coagulation factors and inhibitors.