Differential increase in the maternal serum concentrations of the placental proteins human chorionic gonadotrophin, pregnancy-specific beta 1-glycoprotein, human placental lactogen and pregnancy-associated plasma protein-A during the first half of normal pregnancy, elucidated by means of a mathematical model.

Abstract

The present study was performed to compare the increase in maternal serum concentrations of four placental proteins during the first half of 240 normal pregnancies. The proteins were pregnancy-associated plasma protein-A (PAPP-A), human chorionic gonadotrophin (HCG), human placental lactogen (HPL) hormone, and pregnancy-specific beta 1-glycoprotein (PSG), all produced by trophoblast cells. The median increases were observed to be very close to exponential growth curves. Based on simple assumptions, these growth curves could be explained as being solely dependent on the growth of the placenta. The assumptions were that the proteins were produced in the placenta at a constant rate per gram of placental cell mass and secreted into the circulation shortly after synthesis. Our investigations showed that for two of the proteins, PSG and HPL, the rate constants were, in fact, close to the reported growth rate of the placenta, whereas the PAPP-A production rate constant was significantly higher than those of the others. The production curve for HCG was very different from that of the other proteins. PAPP-A and HCG must therefore have more complicated mechanisms for regulating the production. An equation was constructed that permitted estimation of the molar production of the placental proteins per gram of placental cell mass per day during the first half of normal pregnancy. The value was highest for HPL and lowest for PAPP-A.