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In an attempt to track the proliferation/demise of trophoblastic tissues in women following gamete transfer (GT) or in vitro fertilization/embryo transfer (IVF/ET), we have measured levels of human chorionic gonadotropin (hCG) in serum of 180 patients on days 7 and 14 following oocyte pickup (OPU). Serum hCG levels were measured by immunoassay and by a bioassay based on the capacity of the sample to stimulate testosterone secretion by cultured mouse Leydig cells. Based on determinations of bioactive and immunoactive hCG in serum from 18 of 180 patients who subsequently delivered (12 of 73 GT, 6 of 107 IVF/ET; P less than 0.05) and classification of patients in accord with their compliance or noncompliance with these ranges of values, about 70% of all patients in the present study were classified as "pregnant" 7 days following OPU. Based on these same criteria, about 23% were pregnant 7 days later. Biochemical pregnancy rates on days 7 and 14 following GT (near 73 and 27%, respectively) were not different from the respective values following IVF/ET (near 68 and 20%, respectively; P greater than 0.05). The luteotropin bioassay described is highly sensitive to hCG (to 0.02 mIU/ml serum) and appears appropriate to the characterization of proliferation/demise of embryonic tissues during the 14 days after gamete/embryo transfer. In addition, through its representation of the cumulative luteotropic properties of human serum and its insensitivity to biologically inactive hCG subunits, this bioassay appears more appropriate than hCG immunoassay in the monitoring of early embryonic signalling following assisted (or spontaneous) conception in the woman.

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