Antibodies to phospholipids and nuclear antigens in patients with repeated abortions

The frequency of positive tests for antibodies to nuclear antigens (antinuclear, deoxyribonucleic acid, Ro, La, Smith, and ribonucleoprotein) or to phospholipids was investigated in 82 patients with isolated repeated abortions. Patients with a positive antibody test (positive or negative deoxyribonucleic acid antibodies) appeared to be a separate subgroup of those with unexplained repeated abortions from those with antibodies to cardiolipin. A total of 13.1% of the 61 patients with unexplained repeated abortions had elevated levels of IgM and/or IgG anticardiolipin antibody, while none were found in patients with explained abortions (p < 0.1). Enzyme-linked immunosorbent assays for antibodies binding to other phospholipids suggested that sera from patients with repeated abortions who had the lupus anticoagulant contained antibodies that were most often of the IgG class with affinity for negatively charged phospholipids. Binding of IgG but not IgM antibodies to cardiolipin correlated closely with that to other negatively charged phospholipids. The use of clotting tests for the lupus anticoagulant to screen patients with repeated abortions for associated autoantibodies is likely to significantly underestimate the extent of this clinical problem.