Why are newborns prone to jaundice (the basis of physiological jaundice)?

Newborns jaundice because of increased bilirubin production (high haemoglobin at birth and a shorter red cell lifespan, ~70 days vs 120 in adults) combined with immature hepatic bilirubin conjugation (low glucuronyl transferase) in the first few days, plus increased enterohepatic circulation.

Clinical relevance. Understanding the production/clearance imbalance explains why physiological jaundice is so common in newborns.

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Why newborns are prone to jaundice

Physiological jaundice results from a mismatch between bilirubin production and the newborn's capacity to clear it.

Increased production

• High haemoglobin concentration at birth with breakdown of red cells.
• Shorter red cell lifespan in newborns (about 70 days, versus 120 days in adults).

Reduced clearance

• Immature hepatic bilirubin metabolism - low glucuronyl (UDP-glucuronyl) transferase activity in the first few days, so conjugation is less efficient.

Enterohepatic circulation

• Increased enterohepatic circulation of bilirubin (more so with poor feeding or intestinal obstruction).