The antiphospholipid syndrome is the most common cause of acquired thrombo-philia. Identified autoantibodies include lupus anticoagulant and anticardiolipin antibodies. However, there is some evidence that other as yet unidentified auto-antibodies may cause thrombosis and fetal loss in pregnancy.
The lupus anticoagulant is so called because it causes a prolongation of the activated partial thromboplastin time even when diluted (because the autoantibody binds to phospholipid in the assay). However, it is associated with a thrombotic tendency. Anticardiolipin antibodies are detected by using an immunoassay.
Of women with recurrent miscarriage (three or more), 15% have persistently positive results for phospholipid antibodies. If untreated, 90% will have spontaneous abortions or stillbirths in subsequent pregnancies. It is possible that lupus anticoagulant (30% of cases) and anticardiolipin antibodies (70% of cases) are the same autoantibody identified in different assays. Clinical features of the antiphospholipid syndrome are recurrent fetal loss, thrombosis (arterial and venous), thrombocytopenia, haemolytic anaemia, hypertension, pulmonary hypertension and livedo reticularis. Antiphospholipid syndrome is associated with a 5% incidence of thromboembolism or cerebrovascular accident in pregnancy.
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