Jaundice is derived from the French word jaune, which means yellow, and is the term used to describe the yellowish discoloration caused by an excess amount of bilirubin in skin. Bilirubin is a yellowish-red pigment that is the result of red blood cell (RBC) breakdown in the natural RBC aging process, and is normally found in small amounts in the blood. Its appearance in newborns is primarily due to the immaturity of the newborn’s liver, which cannot effectively metabolize the bilirubin and prepare it for excretion into the urine.

When too much bilirubin is made, the excess is dumped into the bloodstream and deposited in tissues for temporary storage. Most jaundice in newborn babies is a normal event and is not critical. In most cases, this jaundice appears between the second and fifth days of life and clears with time, often without treatment. Also, once this type of jaundice disappears, there is no evidence that it will appear again or that it has any lasting effects on the baby.

Physiologic jaundice in healthy term newborns follows a typical pattern. The average total serum bilirubin level usually peaks at 5 to 6 mg/dL (86–103 μmol/L) on the third to fourth day of life and declines over the first week after birth. Bilirubin elevations of up to 12 mg/dL, with <2 mg/dL (34 μmol/L) of the conjugated form, can sometimes occur. Infants with multiple risk factors may develop an exaggerated form of physiologic jaundice in which the total serum bilirubin level may rise as high as 17 mg/dL (291 μmol/L) (Table 8.1).

Other factors that contribute to the development of physiologic hyperbilirubinemia in the neonate include an increased bilirubin load because of relative polycythemia, a shortened erythrocyte life span (80 days compared with the adult 120 days), immature hepatic uptake and conjugation processes, and decreased enterohepatic circulation.