Diagnosis Measurement of circulating antiphospholipid antibodies Clinical criteria Antiphospholipid syndrome is suspected in women with a history of any of the following: ≥ 1 unexplained fetal losses or ≥ 3 unexplained embryonic losses Prior unexplained arterial or venous thromboembolism New arterial or venous thromboembolism during pregnancy Antiphospholipid syndrome is diagnosed by measuring levels of circulating antiphospholipid antibodies (anticardiolipin, beta-2 glycoprotein I, lupus anticoagulant) with positive results on ≥ 2 occasions 12 weeks apart.