Serum concentration of pregnancy specific and pregnancy-associated proteins in early gestation.

PAPP-A, SP1, hCG and alpha 2-PAG were determined in the serum of 17 patients at weekly intervals between 3 and 12 weeks from the last menstrual period; progesterone and 17 beta-oestradiol concentrations were also measured in the same samples. SP1 and hCG concentrations were consistently found to rise steeply from the first time the proteins were detected. PAPP-A, though detectable in early samples from 9 of the patients, started to rise sharply in all cases between 6 and 10 weeks after LMP. Alpha 2-PAG, which was detected in all serum samples, showed no consistent behaviour with advancing pregnancy. In 3 patients, alpha 2-PAG was elevated as early as 3 weeks after LMP, while in others it remained at low levels during the entire interval observed. The correlation between these proteins (except between SP1 and hCG) is therefore poor; and their synthesis or secretion seems to be independently controlled.