Oral contraceptives and thromboembolic disease

Abstract

The average normal incidence of superficial and deep vein thromboembolic disease in women of childbearing age is 2.2 cases per thoursand women per year. Further the incidence of thromboembolic disease is not increased during pregnancy despite the increased secretion of estrogen and progesterone during this period. The antenatal incidence of thromboembolic disease based on 350000 pregnancies is .61 cases per thousand women per year. It should be emphasized that the widely quoted retrospective survey studies can provided only a hypothesis. Cause and effect relationships can never be established as retrospective studies of Vessey and Doll and of Sartwell and coworkers conclude only that the risk of hospital admission for idiopathic deep vein disease is increased and as stated above this is only a hypothesis. Thus risks calculated from this hypthesis are only theoretical projections and relate only to the theoretical risk for hospital admission. The hypothesis provided by retrospective studies is not confirmed by the large volume of prospective data obtained from women using oral contraceptives. Published data demonstrates that in over 1000 women using oral contraceptives for over 1000000 cycles that the incidence of thromboembolic disease is an average of .9 cases per thousand women per year. It is obvious that this incidence is not above the normal incidence. Analysis of the data to estimate the separate incidence of superficial or deep vein involvement did not show an increase in either category despite the fact that the general population of women would have included women with or without predisposing causes to the disease. Also available data do not demonstrate that women with a history of thromboembolic disease are more susceptible to recurrence when using oral contraceptives to the occurrence of thomboembolic disease. At all doses of the estrogens the incidence of thromboembolic disease was not above the average normal rate of 2.2 cases per thousand women per year. This conclusion does not confirm the report of the British investigators who again made an indirect approach to the subject by comparing case reports with estimated sales for different contraceptive products. Many aspects of their study have been criticized by Nanni (Brit. Med. J. 3:644 1974).(Full text)