Concentrations of placental proteins (HPL and SP1) in maternal serum throughout normal pregnancy.

Throughout 65 normal singleton pregnancies 332 blood samples were obtained and analyzed for pregnancy-specific beta 1 glycoprotein (SP1) and human placental lactogen (HPL). The measurement of SP1 in maternal serum was made using radial immunodiffusion, that of HPL by using radioimmunoassay. There was wide variation in the number and timing of blood samples obtained from patients, and therefore the results could not be used to construct a regression curve by the usual methods applied to independent measurements. Consequently only one value per patient was chosen at random as a basis for calculations. A second degree polynomial for the logarithm of the serum concentrations yielded an optimal fit for both parameters. Tolerance intervals of 90% were calculated for use in future studies.