Abstract
The influence of fetal sex on human chorionic gonadotropin IhCG) in cord and peripheral maternal blood was studied at delivery in 57 twin and 66 singleton uncomplicated pregnancies. In twin pregnancies the hCG levels were about twice as high in female-female and in female-male vis-à-vis male-male combinations in both maternal and cord blood. In singleton pregnancies the hCG levels were significantly higher in maternal and in cord blood in cases of female vis-his male infants. The ratio of maternal hCG/placental weight was also highest in the twin pregnancies when one or both infants were female. This suggests a “female effect”, possibly genetically based.