Introduction
Jaundice is seen in about 60% of term and 80% of preterm babies in the first week. Most is harmless, but high unconjugated bilirubin can enter the brain (kernicterus), and conjugated jaundice can be the first sign of liver disease such as biliary atresia.
Bilirubin in brief
Old red cells → haem → unconjugated bilirubin (fat-soluble, carried on albumin; can cross the blood–brain barrier when free) → the liver conjugates it with glucuronic acid (enzyme UGT1A1) → conjugated bilirubin (water-soluble) into bile → gut. In the newborn's gut, β-glucuronidase splits some back, and it is reabsorbed (enterohepatic circulation).
Physiological jaundice
- Why: many red cells with a short life (70–90 days), immature UGT1A1, more enterohepatic circulation, little gut flora.
- Appears after 24 hours, peaks on days 3–5 in term babies (later and higher in preterm), gone by 2 weeks; unconjugated; baby well.
When jaundice is not physiological
Warning signs:
- Jaundice in the first 24 hours (almost always haemolysis or infection).
- Bilirubin rising fast (over about 85 µmol/L, 5 mg/dL, a day) or above the treatment line for age in hours.
- Prolonged: over 14 days in term, over 21 days in preterm babies.
- Conjugated bilirubin above 17 µmol/L (1 mg/dL), pale stools, dark urine.
- An unwell baby: poor feeding, lethargy, fever.