Reciprocal changes in serum levels of immunoglobulins (IgG, IgA, IgM) and complements (C3, C4) in normal pregnancy and after delivery.

Sequential changes in serum levels of IgG, IgA, and IgM, and C3 and C4 during and after pregnancy were studied in 8 healthy women. Serum IgG decreased gradually during pregnancy, but increased markedly during the six months following delivery. Serum IgA and IgM levels also showed patterns similar to IgG. In contrast, C3 and C4 levels increased significantly and reached maximum levels in the last trimester during pregnancy, but decreased gradually for six months after delivery. Reciprocal changes between immunoglobulins and complements were clarified for the first time, and were suggestive of a compensatory autoregulatory mechanism in the suppression of the humoral immune system during pregnancy.