Blood SC5b-9 complement levels increase at parturition during term and preterm labor

Abstract We explored the hypothesis that complement, an innate and adaptive immune effector, is active in the plasma of parturient women and is deposited on fetal membranes collected after delivery. A cross-sectional study was designed to evaluate complement activity at parturition. Pregnant women ( n  = 97) between 15 and 41 years of age were enrolled in a hospital protocol during the perinatal period to assess both SC5b-9 complement activity in blood and complement deposition on fetal membranes during parturition. Soluble SC5b-9 complement activity in plasma fractions was measured using a standard enzyme-linked immunosorbent assay (ELISA) that included specific anti-complement antibodies. Complement deposition on membranes was analyzed using immuno-dot blots and immunohistochemistry. Soluble SC5b-9 complement complex levels were increased in the plasma of women during term labor (TL; median 3361; range 1726–5670 ng/mL), preterm labor (PL; median 2958; range 1552–7092 ng/mL), and preterm premature rupture of membranes (PPROM; median 2272; range 167–6540 ng/mL) compared with pregnant women who were not in labor (P; median 1384; range 174–4570 ng/mL; P