Interrelationships of human chorionic gonadotropin, human placental lactogen, and pregnancy-specific beta 1-glycoprotein throughout normal human gestation.

Human chorionic gonadotropin (hCG), human placental lactogen (hPL), and pregnancy-specific beta 1-glycoprotein (PSBG) were measured by radioimmunoassay in 270 samples of serum from women with uncomplicated pregnancies. All three proteins were significantly correlated with each other in individual samples of serum and with the estimated trophoblastic mass during the first trimester. No significant correlation could be demonstrated between the concentrations of hCG and PSBG in maternal serum during the second or third trimesters or between the concentrations of hCG and hPL during the second trimester. Levels of PSBG and hPL in serum were significantly correlated throughout all three trimesters. These findings suggest that the secretion of hCG, hPL, and PSBG may be regulated by similar control mechanisms during the first trimester of pregnancy. However, after this period, the factors that modulate the production of hCG differ from those that regulate the production of hPL and PSBG.