Serum concentration of pregnancy-associated plasma protein A in the first trimester of pregnancy

Serial assays of pregnancy-associated plasma protein A were done in 12 subjects before the first missed menstrual period through 10 to 16 weeks' gestation. It was found that the concentration of pregnancy-associated plasma protein A remained at prepregnancy levels until 6 to 10 weeks after the last menstrual period. Thereafter the concentration increased rapidly. It is surmised that pregnancy-associated plasma protein A is a maternal protein, the synthesis of which is stimulated by pregnancy.