Jaundice in newborns is one of the most common reasons for extra days in hospital and for readmission in the first weeks. Its yellow tinge on the skin and whites of the eyes is visually striking, and parents are often alarmed by it. For most babies, it is a benign part of the adaptation from fetal to newborn life and requires nothing more than monitoring and, often, encouragement to feed well.
For a minority of babies, bilirubin levels rise high enough to require phototherapy – treatment under blue-spectrum lights – and in rare untreated cases, high bilirubin can damage the brain. Knowing when jaundice is normal, when treatment is needed, and when dark urine or pale stools signal something more serious allows parents to advocate effectively for their baby's care.
Healthbooq (healthbooq.com) covers newborn health and the hospital and home setting in the first weeks.
Why Newborns Get Jaundice
Bilirubin is the yellow pigment produced when red blood cells are broken down. Newborns have a higher concentration of red blood cells than adults (because fetal haemoglobin carried more oxygen in the womb, where oxygen is less available), and they break down these cells rapidly after birth. The newborn liver is immature and cannot process and excrete bilirubin as quickly as it is produced, leading to accumulation in the blood and tissues – which produces the yellow colour.
This physiological jaundice is normal and expected. It typically appears on day 2-3, peaks around day 4-5, and resolves within 10-14 days in term babies (and up to 21 days in breastfed babies, where a component of jaundice is related to factors in breast milk that slow bilirubin conjugation – this is breast milk jaundice, which is benign and requires no change to breastfeeding).
Jaundice appearing within 24 hours of birth is not physiological and requires urgent investigation – the most common cause is haemolytic disease of the newborn (incompatibility between maternal and fetal blood types, typically Rhesus or ABO incompatibility), which can cause very rapid bilirubin rise.
Risk Factors for Significant Jaundice
Higher bilirubin levels are more likely in: premature infants (more immature liver function); breastfed infants who are not feeding well in the early days (reduced bilirubin excretion due to reduced bowel movements); infants with haemolytic conditions; and infants who are bruised (cephalhaematoma) from birth trauma (more red blood cells to break down).
Family history of jaundice requiring treatment in a previous sibling, certain ethnic groups (particularly East Asian heritage), and male sex are also associated with higher bilirubin levels.
Monitoring
NICE guideline CG98 recommends that all babies are assessed for jaundice risk before discharge and that any baby with clinically visible jaundice (detectable by pressing the skin and looking for yellow under normal lighting) has a total serum bilirubin measured within 6 hours. Visual assessment alone is unreliable (particularly in darker-skinned infants, where jaundice is less visible on the skin); transcutaneous bilirubin meters (a device held against the skin) can screen rapidly and guide decisions about blood testing.
The NICE bilirubin threshold charts (CG98, updated in 2023) show treatment thresholds based on the baby's postnatal age in hours and gestational age. These charts account for the fact that the same bilirubin level is more concerning at 24 hours of age than at 72 hours, and more concerning in a premature baby than a term baby.
Phototherapy
Phototherapy works by converting bilirubin in the skin to a water-soluble form (lumirubin) that can be excreted without conjugation by the liver. Blue-spectrum LED panels or biliblankets (flexible pads placed under the baby) are used. The baby is exposed with as much skin as possible uncovered, with eye protection applied.
Phototherapy is very effective and usually brings bilirubin below treatment thresholds within 24-48 hours. Breastfeeding continues during phototherapy; the baby is removed from the light for feeds. Hydration is important (adequately fed babies excrete bilirubin more quickly).
Exchange Transfusion
If bilirubin rises above exchange transfusion thresholds (significantly higher than phototherapy thresholds), intensive phototherapy is used first and if this fails to halt the rise, an exchange transfusion may be required. Exchange transfusion involves replacing the baby's blood with donor blood in small sequential aliquots, rapidly reducing bilirubin. It is performed in a neonatal intensive care unit.
Kernicterus
Kernicterus is bilirubin-induced brain damage, occurring when unconjugated bilirubin crosses the blood-brain barrier and deposits in specific brain regions (basal ganglia, hippocampus, brainstem nuclei). Acute bilirubin encephalopathy causes poor feeding, hypotonia, arching, high-pitched cry, and in severe cases, seizures, coma, and death. Chronic kernicterus causes athetoid cerebral palsy, hearing loss, and upward gaze palsy. It is preventable with appropriate monitoring and treatment and is now very rare in the UK.
When Jaundice Signals a Serious Problem
Dark urine (instead of pale or colourless) and pale/white/clay-coloured stools in a jaundiced baby signal conjugated (obstructive) jaundice – a different mechanism in which bile cannot flow from the liver into the gut. This can indicate biliary atresia, neonatal hepatitis, or metabolic liver disease. Conjugated jaundice requires urgent investigation; biliary atresia requires surgery before 8 weeks for the best outcomes (Kasai portoenterostomy). Any jaundice persisting beyond 14 days in a term baby or 21 days in a preterm baby requires a split bilirubin measurement to check for conjugated jaundice.
Key Takeaways
Neonatal jaundice (yellowing of skin and eyes due to elevated bilirubin) affects around 60% of term newborns and 80% of preterm newborns in the first days of life. Most physiological jaundice is mild and requires no treatment, resolving within 2 weeks. Phototherapy (blue-spectrum light that breaks down bilirubin in the skin) is the main treatment when bilirubin rises above treatment thresholds based on postnatal age and gestational age. Very high bilirubin (above exchange transfusion thresholds) can cause bilirubin-induced brain damage (kernicterus), which is now rare in the UK due to monitoring and treatment. NICE guideline CG98 provides bilirubin threshold charts for treatment decisions.
