ObjectiveTo determine whether antiphospholipid antibodies other than lupus anticoagulant and anticardiolipin are associated with recurrent pregnancy loss.MethodsSera from three groups of women were studied: 1) 147 women with recurrent pregnancy loss but no clinical signs or symptoms of autoimmune disease who tested negative for lupus anticoagulant and medium-to-high levels of immunoglobulin G anticardiolipin antibodies; 2) 104 healthy, fertile controls of similar age and gravidity; and 3) 43 women with well-characterized antiphospholipid syndrome. Serum antibody binding against six phospholipids (cardiolipin, phosphatidic acid, phosphatidylserine, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol) was determined using enzyme-linked immunoassays, and results were normalized using an anticardiolipin standard.ResultsTwenty-six (18%) women with recurrent pregnancy loss and nine (9%) controls tested positive (above the 99th percentile) for antiphospholipid antibodies. Sera from five (3.4%) women with recurrent pregnancy loss and four (3.8%) controls demonstrated binding to phospholipid antigens other than cardiolipin. In contrast, binding to phospholipid antigens was demonstrated in sera from more than 90% of women with antiphospholipid syndrome. Among women testing positive for antiphospholipid antibodies, the median positive value for women in the antiphospholipid syndrome group was significantly higher than for those with recurrent pregnancy loss or normal fertile controls.ConclusionsWomen with recurrent pregnancy loss are no more likely than fertile controls to have elevated levels of antiphospholipid antibodies once lupus anticoagulant, anticardiolipin, and an obvious clinical history of autoimmune disease have been excluded. Testing for antiphospholipid antibodies other than lupus anticoagulant and anticardiolipin is not clinically useful in the evaluation of recurrent pregnancy loss.