Etiology of physiologicaljaundice In the first few days after birth, hemoglobulin concentration falls rapidly Red cell life span of newborn infants is 70 days which is much shorter than that of adults(120 days) Hepatic bilirubin metabolism is less efficiencyEtiology of physiological jaundice In the first few days after birth, haemoglobulin concentration falls rapidly. Red cell life span of newborn infants is 70 days which is much shorter than that of adults(120 days). Hepatic bilirubin metabolism is less efficiency