Jaundice in Preterm Babies

Why preterm jaundice is a different problem

Jaundice is the yellowing caused by bilirubin, a pigment made when red blood cells break down. Newborns make a lot of it and clear it slowly, which is why most babies go a bit yellow in the first week.

Preterm babies do the same thing, only more so, and for reasons that stack up. The liver enzyme system that processes bilirubin is less mature. Feeding is slower to establish, which slows the route out through the gut. Bruising from the birth and repeated blood tests add to the load. And the blood-brain barrier is more permeable, so bilirubin reaches the brain at lower blood levels than it would in a term baby.

That last point is the whole reason the rules are different. Kernicterus — permanent brain injury from very high bilirubin — is recognised to occur at lower levels in preterm babies. So the safe level is lower, and treatment starts sooner.

NICE puts prematurity at the top of its risk list: gestational age under 38 weeks is the first of the four factors CG98 says makes a baby "more likely to develop significant hyperbilirubinaemia", alongside a previous sibling who needed phototherapy, exclusive breastfeeding, and jaundice visible in the first 24 hours.

The thresholds are a graph, not a number

Parents almost always want the number: at what level does my baby need lights? There is no single number, and the reason matters.

NICE CG98 publishes a threshold table, and that table is explicitly labelled as consensus-based thresholds "for management of babies 38 weeks or more gestational age". For babies below 38 weeks, NICE uses treatment threshold graphs instead, which are gestation-specific: a separate line for each gestational age, plotted against your baby's age in hours. A baby born at 28 weeks and a baby born at 34 weeks are read off different lines, and both are read off lower lines than a term baby.

Which is why this page will not give you a figure. A bilirubin result has to be read against the right line for the right gestation at the right hour of life, and a number that was reassuring for someone else's baby could be a treatment level for yours. NICE also warns that bilirubin assays vary between manufacturers and that teams should check with their own laboratory when interpreting thresholds. If you want to understand where your baby sits, ask the team to show you the graph with your baby's result plotted on it. They will — it is a normal request and it is far more informative than a number on its own.

Blood tests instead of the forehead meter

Term babies are often screened with a transcutaneous bilirubinometer, the handheld device pressed to the forehead or sternum. NICE says to use serum bilirubin — an actual blood test — for babies with a gestational age of less than 35 weeks. The meter is not accurate enough at these gestations.

NICE also says to measure serum bilirubin urgently, within two hours, in any baby with suspected or obvious jaundice in the first 24 hours of life, and to keep repeating it every six hours until the level is both falling and below the treatment threshold. Jaundice in the first day of life is never normal at any gestation.

This is why your baby is having heel pricks for jaundice when a term baby down the corridor is having a forehead scan. It is not extra caution for its own sake.

Phototherapy on a neonatal unit

Treatment is phototherapy: light of a particular wavelength that converts bilirubin in the skin into a form the body can excrete without the liver processing it. On a neonatal unit it is usually delivered as overhead LED lights above the incubator, sometimes with a fibreoptic pad or blanket underneath as well. Your baby wears eye protection or is nursed under a tinted headbox — NICE restricts the tinted headbox alternative to babies of 37 weeks or more, so a preterm baby will usually be in eye pads.

Preterm babies are more likely to need intensified phototherapy, meaning more than one light source, and more likely to need it for longer. Levels are rechecked during treatment, and phototherapy is stopped once the level has fallen a defined distance below the threshold, with a further check afterwards for rebound.

Exchange transfusion — replacing the baby's blood in small amounts — is the treatment for levels that phototherapy cannot control, and it is uncommon. NICE requires that parents are told why it is being considered, what it involves, that it needs an intensive care bed, and when they will be able to see and hold their baby afterwards.

The 21-day rule

Here is the difference that follows you home. For a baby of 37 weeks or more, jaundice lasting longer than 14 days triggers investigation for prolonged jaundice. For a baby born before 37 weeks, NICE sets that trigger at 21 days.

Preterm jaundice is expected to last longer, so a still-slightly-yellow four-week-old who was born at 32 weeks is not automatically a problem. The tests done at that point look for the things that are a problem — principally a raised conjugated bilirubin, which can indicate liver or bile duct disease.

The signs that should never wait for a scheduled review, at any gestation: pale, chalky stools, dark urine that stains the nappy, a baby who is difficult to wake or feed, or jaundice that is deepening rather than fading. Those need a call the same day.

What you can and cannot do

You can feed frequently, because bilirubin leaves through the gut and feeding drives that. You can keep expressing if your baby is not yet feeding by mouth. You can ask to keep doing skin-to-skin, because phototherapy breaks for cares and cuddles are usually possible and should be discussed rather than assumed away.

What does not work: sunlight through a window is not phototherapy and risks burning and chilling a preterm baby, and stopping breastfeeding is not a treatment. The NHS advice remains to continue breastfeeding through jaundice unless your team specifically tells you otherwise.