Antithrombin III and procoagulant activity: sex differences and effects of the menopause.

Among participants in the Northwick Park Heart Study, antithrombin III activity was lower in pre-menopausal women than in men of the same age. In the women, however, the menopause was associated with a significant increase in antithrombin III, mean levels in these older women then exceeding levels in men of the same age. The occurrence of the menopause was also accompanied by large increases in factor VII coagulant activity, VIIc, and in plasma fibrinogen, these increases being greater in those experiencing a natural menopause than in those whose menopause was artificial. Sex differences in antithrombin III may form part of the explanation for the observed differences between men and women in their experience of ischaemic heart disease (IHD) and also for the contrasting effects of oral contraceptives and of hormone replacement therapy on the risk of thromboembolic disease.