C3 and C4 complement components and acute phase proteins in late pregnancy and parturition.

To determine whether changes in complement or acute phase proteins can predict onset of labour, complement components C3 and C4, alpha-1-antitrypsin, and alpha-1-acid glycoprotein were measured serially in the third trimester of pregnancy and throughout labour in 11 women. C-reactive protein (CRP) concentration, C3 conversion products, and factor B activation was studied in five pregnancies one week before delivery, during labour, and six weeks after delivery. C3, C4, and CRP concentrations were unchanged and there was no evidence of complement conversion, either immediately before or during labour, by the classical or alternative pathways. A wide variation among subjects but a small variation within subjects for all proteins assayed was noted. It is important to use serial rather than cross sectional biochemical data when determining normal physiological patterns in pregnancy. The proteins measured have no predictive value in the timing of the onset of normal labour.