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Neonatal jaundice

e) Breastfed infants are more likely to develop physiological jaundice within the 1st week of
life. Prolonged jaundice, that is jaundice persisting beyond the first 14 days, is also seen more
commonly in these infants. The mechanism for this ‘breast milk jaundice syndrome’ is still
not completely understood and the condition appears to be generally harmless.
f) Jaundice may also have other, non-physiological, causes, including blood group
incompatibility (Rhesus, ABO or similar problems), other causes of haemolysis, sepsis,
bruising and metabolic disorders. Gilbert's and Crigler–Najjar syndromes are rare causes of
neonatal jaundice. Deficiency of a particular enzyme, glucose-6-phosphate-dehydrogenase
(G6PD), can cause severe neonatal jaundice. G6PD deficiency is more common in certain
ethnic groups and runs in families. Congenital obstruction and deformities affecting the
biliary system, such as in the condition known as biliary atresia, cause an obstructive
jaundice associated with conjugated hyperbilirubinaemia. This condition needs specialist
management and surgical treatment.
g) In young babies, unconjugated bilirubin can penetrate across the membrane that lies
between the brain and the blood (the blood-brain barrier). Unconjugated bilirubin is
potentially toxic to neural tissue (brain and spinal cord) because it acts as a ‘cell poison’
slowing essential processes. Entry of unconjugated bilirubin into the brain can cause both
short-term and long-term neurological dysfunction. Acute problems include lethargy,
abnormal muscle tone, irritability, temporary cessation of breathing (apnoea) and
convulsions. This presentation is known as acute bilirubin encephalopathy. This deposition of
bilirubin causes a yellow staining of a particular part of the deep neural tissue (the deep grey
matter) within the brain; this staining is referred to as ‘kernicterus’. The term kernicterus is
also used to denote a group of signs typical of chronic bilirubin encephalopathy. These signs
include athetoid cerebral palsy, hearing loss, visual and dental problems. The exact level of
bilirubin that is likely to cause neurotoxicity in any individual baby varies, and depends on
the interplay of multiple factors that probably include acidosis, postnatal age, rate of rise of
bilirubin level, serum albumin concentration, and whether the baby has another illness at the
time (including infection).
h) Although neonatal jaundice is very common, kernicterus is very rare. There is a poor
correlation between levels of bilirubin in the body and the clinical features of bilirubin
encephalopathy. There seems to be tremendous variability in susceptibility towards bilirubin
encephalopathy among newborns for a variety of unexplained reasons. However, there are
certain factors that probably influence the passage of bilirubin into the brain and hence
increase the risk of acute bilirubin encephalopathy. These include dehydration, preterm birth,
respiratory distress, sepsis, hypoxia, seizures, acidosis and hypoalbuminaemia. The rate of
rise of the level of bilirubin is probably important, hence the increased risk of kernicterus in
babies with haemolytic disease such as G6PD deficiency or Rhesus haemolytic disease.
i) The correlation between actual bilirubin levels and kernicterus is poor for the various reasons
discussed above in 3 g and h. Kernicterus in healthy term babies with none of the factors (as
described above) is virtually unknown below a threshold level of 425 micromoles of bilirubin
per litre of serum, but the number of cases rises above this threshold level and the risk of
kernicterus is greatly increased in full term newborns with bilirubin levels above
515 micromol/litre. Kernicterus is also known to occur at lower levels of bilirubin in full term
babies who have any of the factors described in 3 h.
j) Levels of bilirubin can be controlled by placing the baby under a lamp emitting light in the
blue spectrum; this is known as phototherapy. Light energy in the appropriate part of the
spectrum converts the bilirubin in the skin to a harmless form that can be excreted in the
urine. Phototherapy has proved a very efficient safe and effective treatment for jaundice in
newborns, reducing the need to perform an exchange transfusion of blood (the only other
means of removing bilirubin from the body).
k) Clinical recognition and assessment of jaundice can be difficult. This is particularly the case
in babies with darker skin. Once the diagnosis is made, there is uncertainty about when to
treat raised bilirubin levels and there are variations in the use of phototherapy, exchange
transfusion and other treatments. There is a need for more uniform, evidence-based practice,
and for more widespread consensus-based practice in areas lacking evidence.

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