Problems encountered in the measurement of pregnancy-specific beta1-glycoprotein

Evidence is presented here that variants of the human trophoblastic plasma protein, pregnancy-specific beta1-glycoprotein (PSbetaG) are detectable in plasma samples from a small percentage of subjects and may be recognised by their capacity to form indistinct immunoprecipitates and give artificially low levels when measured by radioimmunoassay. Urinary PSbetaG shows a marked degree of heterogeneity and is difficult to measure using conventional immunoprecipitation assay techniques. By radioimmunoassay, late pregnancy urinary PSbetaG concentrations have been found to be in the range 0.35 to 6.9 microgram/ml, approximately 3% of the term plasma concentrations.