SERUM CONCENTRATIONS OF HUMAN CHORIONIC GONADOTROPHIN AND ITS ALPHA AND BETA SUBUNITS. 1. DURING NORMAL SINGLETON AND TWIN PREGNANCIES

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Abstract
SUMMARY: Homologous radioimmunoassays have been developed for native hCG and its α and β subunits. Their specificities were assessed by analysis of the inhibition curves and by gel filtration of purified preparations of native hCG, hCGα and hCGβ, and of sera from pregnant women, on Sephadex G 100. Gel filtration data indicated a true cross‐reaction of native hCG in the hCGβ and hCGα assays of 0.5 and 0.35%, respectively. After validation of the RIA procedures for unfiltered serum assays, we have demonstrated that in 311 maternal sera obtained in 207 normal singleton pregnancies, free circulating hCGα increases continuously, whereas free hCGβ and native hCG peak between the 8th‐10th week. The ratio (hCGβ/hCG) x 100 is greatest during the first trimester (2–3%) and decreases thereafter to around 1%. The ratio (hCGα/hCG) x 100 is < 1% at the beginning of pregnancy, 2% at 14 weeks and 15–20% from the 23rd week onwards. The levels of hCG and its subunits are higher in fifty‐two samples obtained throughout normal twin pregnancies than in corresponding single pregnancies, but the ratios subunit: hCG are the same, suggesting qualitatively similar placental secretion in both types of pregnancy. Analysis of pregnancy sera by gel filtration and assay of hCG and subunits in eluant fractions confirmed that free α and β subunits are present in the circulation and that hCGα rises while hCG and hCGβ fall in late pregnancy. Heterogeneity of the circulating hCGβ subunit is also demonstrated.