Some qualitative differences of hCG in serum from early and late pregnancies and trophoblastic diseases

Twenty-four sera were obtained from women in the first and third trimester of pregnancy, women with gestational choriocarcinoma, and men with testicular hCG-producing tumours. The hCG-activity was measured by an in vivo bioassay (B) based upon the increase in mouse uterine weight. The sera were also analysed by three immunoassays (I), one for hCG, one for alpha-hCG subunits, and one for beta-subunits. All sera were also subjected to electrophoresis in 0.17% agarose suspension in 0.075 mol/l sodium veronal buffer at pH 8.6, and median charge, expressed as median mobility, was estimated for hCG. The metabolic clearance rate (MCR) of hCG in serum in early and late pregnancy and from one patient with choriocarcinoma was measured in mice. The B/I ratio was lower and the forms of hCG were less negatively charged in late pregnancy compared with early pregnancy. The lower B/I ratio might be due to the higher MCR of hCG in the test animal in the in vivo bioassay. The B/I ratio in choriocarcinoma was higher than in early pregnancy. However, the median charge of hCG was almost identical in these two groups. The most negatively charged forms of hCG were found in the men with testicular tumours. The four groups: early pregnancy, late pregnancy, gestational choriocarcinoma, and testicular tumours could be differentiated by measuring the median charge and the B/I ratio of hCG in serum. The production, later in pregnancy, of forms of hCG which disappear faster from the circulation might partially explain the lower hCG concentration in serum at this stage of gestation.