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

Abstract

Homologous radioimmunoassays [RIA] were developed for native hCG [human chorionic gonadotropin] and its .alpha. and .beta. subunits. Their specificities were assessed by analysis of the inhibition curves and by gel filtration of purified preparations of native hCG, hCG.alpha. and hCG.beta., and of sera from pregnant women, on Sephadex G 100. Gel filtration data indicated a true cross-reaction of native hCG in the hCG.beta. and hCG.alpha. assays of 0.5 and 0.35%, respectively. After validation of the RIA procedures for unfiltered serum assays, in 311 maternal sera obtained in 207 normal singleton pregnancies, free circulating hCG.alpha. increases continuously, whereas free hCG.beta. and native hCG peak between the 8th-10th week. The ratio (hCG.beta./hCG) .times. 100 is greatest during the 1st trimester (2-3%) and decreases thereafter to .apprx. 1%. The ratio (hCG.alpha./hCG) .times. 100 is < 1% at the beginning of pregnancy, 2% at 14 wk and 15-20% from the 23rd wk onwards. The levels of hCG and its subunits are higher in 52 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 .alpha. and .beta. subunits are present in the circulation and that hCG.alpha. rises while hCG and hCG.beta. fall in late pregnancy. Heterogeneity of the circulating hCG.beta. subunit is also demonstrated.