Jaundice index (serum bilirubin value) The highest normal neonatal jaundice index is about 51.3 μmol/L (3mg/dl), peaking about 4 days after birth, generally not more than 171-205 μmol/L (10-12mg/dl), preterm infants do not exceed 256.5 μmol/L (15mg/dl), and then gradually recover. Most newborns start to have mild yellow staining on the skin, oral mucosa and white part of the eyes 2~3 days after birth, while the palms of hands and feet usually do not have yellow staining, and the yellow staining is heaviest on 4~6 days, and then gradually decreases. During this period, the child has no abnormalities other than jaundice, and if the blood is checked, the total serum bilirubin concentration does not exceed 205 micromol/l for full-term infants and 256 micromol/l for preterm infants, a phenomenon known as “physiological jaundice”. The main causes of physiological jaundice (1) the fetus to survive, need a large number of red blood cells from the mother to transport sufficient oxygen; after birth, the respiratory system began to work, oxygen supply is sufficient, no longer need too many red blood cells to transport oxygen, resulting in increased destruction of red blood cells, excessive bilirubin production. (2) The metabolic function of the liver of newborns is not yet perfect, and the normal intestinal flora has not yet been established, which cannot further transform bilirubin and excrete it out of the body. As a result, excessive bilirubin accumulates in the blood, and when it exceeds a certain amount, it stains the skin, mucous membranes and the whites of the eyes yellow.