Determination of the stage of gestation by the assay of chorionic gonadotrophin and Schwangerschaftsprotein 1.

Serial assays of Schwangerschaftsprotein 1 (SP1), SP1 alpha, SP1 beta and human chorionic gonadotrophin were performed in 12 subjects from ovulation until the pregnancies had reached 16 weeks. From these data formulae were devised for deducing the stage of gestation from the concentration of the placental protein. These formulae were then tested by assays on 34 women not included in the original study. Assays of hCG do not give reliable indications of the stage of gestation when this has progressed beyond 9-10 weeks but SP1 assays give predictions of gestation corresponding closely to that derived from the last menstrual period up to 16 weeks gestation.