Amniotic fluid and plasma concentrations of pregnancy-associated plasma protein-A (PAPP-A) throughout pregnancy: comparison with other fetoplacental products.

The development of a sensitive radioimmunoassay has enabled measurements of pregnancy-associated plasma protein-A (PAPP-A) to be performed from early pregnancy. The present paper compares the plasma concentrations of PAPP-A with the levels of two trophoblastic proteins, human placental lactogen (hPL) and the beta-subunit of human chorionic gonadotrophin (beta-hCG), with a steroid of fetoplacental origin, total oestriol (total E3), and with a fetal protein, alpha-fetoprotein (AFP). PAPP-A was also measured in amniotic fluid and in maternal urine. In contrast with the secretion of the other substances studied, which either reach a plateau or even decrease during the last 4 weeks of pregnancy, PAPP-A steadily increased in the maternal circulation from 7 to 40 weeks gestation. It is proposed that PAPP-A production is either not related to placental mass or that PAPP-A is not of trophoblastic origin. The increase of PAPP-A in amniotic fluids parallels the increase in maternal blood; virtually no PAPP-A is excreted in urine.