Human Chorionic Gonadotropin Pattern in Serum and Its Relation to the Sex of the Fetus

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Abstract
The pattern of the human chorionic gonadotropin (HCG) level in serum throughout pregnancy has been established in longitudinal studies on 20 healthy women. Blood samples obtained at intervals of 3-4 weeks have been analyzed by means of a quantitative immunoassay procedure based on complement fixation. A biphasic course of the HCG level has been confirmed; a relatively sharp and acute peak in the first trimester and a comparatively small rise in the last 3 months are separated by an intervening low-level period in midpregnancy. A considerable individual scatter of the HCG levels is observed, particularly in the last trimester. A relation has been found between the sex of the fetus and the height of the HCG level during this period. In women with low HCG values there is a predominance of male fetuses, and in subjects with high levels a preponderance of female fetuses is observed. The statistical significance for a difference between male-fetus and female-fetus pregnancies is at the 0.5% level.