Neonatal physiologic jaundice results from simultaneous occurrence of the following two phenomena : • Bilirubin production is elevated because of increased breakdown of fetal erythrocytes. This is the result of the shortened lifespan of fetal erythrocytes and the higher erythrocyte mass in neonates. Larger prospective studies in diverse populations are needed to determine the rates of early breastfeeding discontinuation in jaundiced infants.
Hepatic excretory capacity is low both because of low concentrations of the binding protein ligandin in the hepatocytes and because of low activity of glucuronyl transferase, the enzyme responsible for binding bilirubin to glucuronic acid, thus making bilirubin water soluble (conjugation). It is estimated that 60% of term newborns develop jaundice and 2% reach a TSB concentration greater than 340 µmol/L .