Anticardiolipin antibodies and complement in ninety-nine women with habitual abortion.

Immunologic investigations were performed on sera from 99 women with habitual abortion (three or more consecutive miscarriages). All were considered healthy and clinical investigations had not revealed any cause for the miscarriages. Sixty-eight were considered to have primary habitual abortion whereas 31 had secondary habitual abortion. Increased anticardiolipin antibody levels were found in 42 patients. None had a primary diagnosis of systemic lupus erythematosus, but at follow-up studies one of them fulfilled the diagnostic criteria of systemic lupus erythematosus. Ten sera, all from patients with primary habitual abortion, showed high anticardiolipin antibody values (greater than or equal to 10 units) concomitant with significantly lower levels of complement factor C4 than those found in sera with moderate or normal anticardiolipin antibody levels. There was no indication of genetic defects explaining the low C4 values, which could be explained at least in part by an activation of complement by the classical pathway.