Classical complement activation induced by pregnancy: Implications for management of connective tissue diseases

Abstract

Aims: to determine the effect of pregnancy on C4d concentrations and to assess whether C4d remains a useful disease activity marker in the management of connective tissue diseases during pregnancy. Methods: Plasma C3, C4, and C4d concentrations were measured in 83 women at various stage of normal pregnancy and compared with those in 80 non-pregnancy controls. Results: C3 concentrations in the pregnant women were significantly raised (p = 0.0001) and the C4 concentrations were reduced (p = 0.0007), and accompanied by a significant increase in C4d (p = 0.0001). The C4d:C4 ratio was higher in the pregnant women (p = 0.0001). Conclusions: Pregnancy induces activation of the classical complement pathway. C4d concentrations cannot be used to monitor disease activity in patients with connective tissue diseases during pregnancy.