PubMed1996
Oral contraceptives increase the natural incidence of venous thromboses of 1-2/10,000 women per year 3-to 4fold. Recent investigations have shown that during intake of desogestrel or gestodene containing formulations the risk is twice that with older low-dose ovulation inhibitors. This difference is larger in first time users than in women who had previously used an oral contraceptive. During pregnancy, the incidence of thromboses rises up to 10/10,000 women-years and post partum up to 40/10,000 women-years. In about 60 % of thromboses no causal explanation can be found. It is suggested that in 40 % of all cases an inherited thrombophilia is present. Among the hereditary types of thrombophilia, the resistance against activated protein C (APC-resistance) represents nearly 50 %, while altogether 15 to 20 % is based on a deficiency of antithrombin III, protein C or protein S. APC-resistance the prevalence of which is 3-5 % in the general population, increases the risk of thrombosis 8fold and in users of oral contraceptives 35fold. Protein C-deficiency (prevalence 0.1-0.5 %) increases the risk of thrombosis 9fold and in users of oral contraceptives 15fold, while antithrombin III-deficiency (prevalence 0.02-0.05 %) enhances the risk in pill-users 8fold. Ovulation inhibitors do not influence risk of thrombosis in women with protein S-deficiency. Antiphospholipid-antibodies the concentration of which may increase during treatment with oral contraceptives, represent a considerably enhanced risk of thrombosis, too. A positive family history (before age of 40 years) indicates an inherent thrombophilia. In these risk groups, the cost/benefit ratio of a selective screening is unfavorable, as at most 70 % of the hereditary thrombophilias can be diagnosed by laboratory analysis, and only very few patients will actually experience a thrombotic event: only 3 of 1000 carriers of APC-resistance will suffer from thrombosis during oral contraception per year. On the other hand, a negative result of laboratory tests does not exclude a hereditary thrombophilic disorder which as yet cannot be substantiated. It is not yet clarified whether a selective screening is superior to a careful assessment of individual and family history. A general screening cannot be justified because of the unfavorable cost/benefit ratio. If the individual or family history or pathological laboratory parameters indicate an enhanced risk of thrombosis, this risk has to be carefully weighed against the consequences of discontinuation of pill use. Those few individuals with risk factors who will experience a thrombosis, cannot be identified in advance. If in patients with thrombophilic disorders and/or other risk factors the use of oral contraceptives represents a particularly high risk, other contraceptive methods should be taken into consideration. If a patient with risk factors decides for the use of oral contraceptives, she has to be informed that in the case of symptoms indicating a thrombosis, the physician has to be consulted immediately. The earlier an appropriate therapy is initiated, the more effectively an acute pulmonary emboli or permanent damages, e.g. the post-thrombotic syndrome, can be prevented.