The influence of pregnancy and oral contraceptive steroids on the concentration of plasma proteins. Studies with a quantitative immunodiffusion method

The concentrations of 11 plasma proteins were determined in 25 women in the third trimester of pregnancy, 31 women who had taken oral contraceptive agents containing synthetic estrogens and progestins for 3 months or longer, and 31 women of comparable ages who served as controls. Sera from fasting subjects were used to determine, by means of quantitative immunodiffusion assay, the level of each individual protein. Pregnancy and treatment with oral contraceptives produced increased mean serum levels of the following proteins: ceruloplasmin, α₁-antitrypsin, transferrin, and β_1A-globulin. The following proteins were decreased in concentration: α₁-acid glycoprotein, haptoglobin, and albumin. The slight decrease in the mean concentration of serum albumin produced by oral contraceptives was not statistically significant. The concentrations of γA-globulin, γM-globulin, and α₂-macroglobulin were not significantly altered by pregnancy or by treatment with oral contraceptives. γG-globulin was significantly reduced in pregnant woman. The effects of oral contraceptives on the concentrations of plasma proteins, although less marked, generally paralleled those produced by late pregnancy. The most striking alterations were noted in serum proteins that are known to be synthesized by the liver, an observation consistent with the significant influences which sex hormones exert on various metabolic activities of this organ.