To the new-born infant the extra-uterine environment presents many new problems. At birth the rosy complexion of the skin is similar to that of a plethoric person. This rosiness, however, is not caused by polycythemia, but is rather an erythema neonatorum and disappears after a few days, only to be replaced by the yellowness of jaundice.
The most generally accepted explanation of the occurrence of icterus neonatorum is that it accompanies the infant's postnatal readjustment from an environment which required polycythemia for oxygenation to one which does not. Because of the change in environment after birth, hemolysis occurs, which is the direct cause of the hyperbilirubinemia. Since the liver is incapable of excreting all of the increased amount of bile pigment in a normal manner, it passes some of it into the blood stream and jaundice results.
According to our observations, polycythemia is absent in the fetus, the red blood
HOLLÓSI C, HORVÁTH Z. HEMOGLOBIN INDEX AND JAUNDICE OF THE NEW-BORN. Am J Dis Child. 1935;49(3):638-641. doi:10.1001/archpedi.1935.01970030084007