| Abstract: | We have validated a direct radioimmunoassay (RIA) which measures the alpha-subunit of human chorionic gonadotropin (hCG) in pregnancy sera in the presence of large amounts of hCG. The levels of alpha-subunit in 124 sera from normal pregnancy women were measured and compared to the levels of hCG measured by a radioreceptor assay (RRA) which utilizes a rat testicular membrane preparation. Unlike hCG, which peaks at the end of the first trimester, the alpha-subunit continues to rise until 36 weeks of pregnancy. During the first half of pregnancy the levels of alpha-subunit remain less than 100 ng/ml whereas in the second half the levels remain less than 200 ng/ml. Three pathologic pregnancies were also studied; on the basis of the hCG determinations, they could not be differentiated from normal pregnancy. In contrast, all determinations of alpha-subunit were abnormally elevated. The concept that placental dysfunctions would cause an early and abnormally high level of alpha-subunit secretion deserves further investigation. |
