Total complement activity in maternal sera, amniotic fluids and cord sera in women with premature labor, premature rupture of membranes or chorioamnionitis.

Total hemolytic complement activity (CH50) was determined in maternal sera, amniotic fluids or cord sera, or all, from 119 patients with preterm uterine contractions, premature rupture of membranes or chorioamnionitis, or all, at 24 to 40 weeks of gestation. The mean CH50 of maternal sera exceeded the mean CH50 of both amniotic fluids and cord sera. The mean CH50 of amniotic fluids exceeded that of cord sera and increased significantly at 32 weeks. This rise preceded that of the mean CH50 of cord sera, which occurred at a fetal weight of approximately 2,500 grams. The mean CH50 of amniotic fluids varied significantly and inversely with that of cord sera. The levels of CH50 in these three fluids did not distinguish between patients with preterm uterine contractions who delivered prematurely and those who delivered at term. The CH50 in patients with premature rupture of membranes did not differ from a control population of women with uncomplicated pregnancies. The mean CH50 of maternal sera was increased in patients with chorioamnionitis but was not predictive of chorioamnionitis. The mean CH50 of maternal sera was decreased in patients who smoked cigarettes and in patients who received intravenous ritodrine.