Hypocomplementemia in the absence of autoantibodies in women with recurrent pregnancy loss.

BACKGROUND Accumulating data suggest an immunopathogenic role for the complement system as a causative element in pregnancy loss (PL). Formation of pathogenic antibodies with activation of the classical pathway may have a role, but this mechanism fails to characterize the majority of cases with recurrent PL. We established the prevalence of hypocomplementemia without circulating autoantibodies in women with recurrent PL. METHODS In a retrospective case control study, 201 women with recurrent PL (two or more PL) and 30 healthy women who had normal pregnancies but no PL were studied. Serum levels of C3, C4, and factor B were determined by nephelometry. Total hemolytic activity of the complement system (CH100) was investigated by radial immunodiffusion test. RESULTS The prevalence of hypocomplementemia [low levels of C3, C4, FB or CH100 (with normal concentrations of C3, C4 and FB)] was significantly higher in women with recurrent PL (22.4%) in comparison with controls (6.6%; p = 0.019). C3, C4, FB hypocomplementemia or low CH100 were observed in 13 (6.5%), 19 (9.4%), 13 (6.5%) and 7 (3.5%) women with recurrent PL, respectively. Among patients with C3, C4, FB or CH100 hypocomplementemia, 10, 18, 12 and 5 patients had no circulating autoantibodies [antinuclear antibodies, anticardiolipin antibodies or antithyroid antibodies], respectively. In all, hypocomplementemia, in the absence of autoantibodies, was observed in 38 (18.9%) women with recurrent PL in a significantly higher frequency than controls (n = 2, p = 0.049). CONCLUSIONS Hypocomplementemia, in the absence of autoantibodies was observed in a group of women with recurrent PL which might suggest a role of the complement system in the pathogenesis of PL in these patients.