Characterization of human chorionic gonadotropin in normal and abnormal pregnancies

In this study circulating human chorionic gonadotropin (hCG) levels in the peri-implantation period of natural cycles of normal women were characterized. The hypothesis that the bioactivity of hCG in abnormal pregnancies is different from that in normal pregnancies was tested daily through serum hCG measurements in two immunoenzymometric assays, a radioreceptor assay and a human luteinizing hormone/human chorionic gonadotropin--cyclic adenosine monophosphate--luciferase bioassay. In normal pregnancies, the levels of immunoreactive and bioactive hCG were higher than in abnormal pregnancies (p < 0.05). In addition, the slopes of the rise in concentration of hCG as measured in all four assays were significantly greater for normal pregnancies than for abnormal pregnancies (p < 0.01). The rate of rise of hCG bioactivity was significantly greater than the rise of immunoreactivity or receptor-binding activity in normal pregnancies, but this difference was not observed in abnormal pregnancies. These results indicate that: (1) A steep rise of bioactive hCG is a consistent feature of the peri-implantation period of normal pregnancies. (2) Abnormal pregnancies had a deficiency in the production of hCG, which was reflected in both the hCG levels and the rate of increase, even in the first week of implantation. (3) Some abnormal pregnancies produced hCG with lower biological activity than the hCG of normal pregnancies.