Kernicterus is caused by a high level of bilirubin in a baby's blood. If left untreated, the bilirubin can then spread into the brain, where it causes long-term damage.
A low-level buildup of bilirubin is normal. This is called mild jaundice, and it gives a newborn a slightly yellowish tint to the skin and sometimes the eyes.
Normally, extra bilirubin is removed from the bloodstream by the liver and kidneys, and it leaves the body in urine and stool. During pregnancy, the mother's body removes the extra bilirubin for the baby. After birth, it takes a few days for the newborn's liver to get good at removing bilirubin from the blood. If you feed your baby every 2 to 3 hours, mild jaundice will usually go away on its own after a few days. But if your baby has any signs of jaundice, you and your doctor will need to watch him or her closely.
If jaundice continues to get worse and is not treated, bilirubin in the blood can build up to a high level. This is when kernicterus becomes a concern. It may be that some babies have health problems that make them more likely to have bilirubin levels that climb to high levels. For example, hemolytic disease, in which a mother's Rh blood factor is not compatible with her baby's, can make a baby produce more bilirubin than normal. Intestinal blockages can make it harder for a baby to remove bilirubin.
What are the symptoms?
Kernicterus has likely already started if a baby has certain symptoms, including:
Extreme sleepiness and lethargy. This means a baby is difficult to wake up from sleep or can't be kept awake. But keep in mind that newborn babies sleep a lot. Lethargy in a newborn is easy to confuse with normal newborn behavior. A lethargic baby does not eat well, does not respond to touching or does not startle from sudden movements, and never seems to fully wake up.
A very high-pitched cry that does not sound normal.
Poor muscle tone. The baby may seem "floppy" and weak. Sometimes this is followed by periods when the baby's muscles flex in a way that is not normal. The baby may be stiff and arch his or her back and head.
A fever that occurs along with any of these other symptoms.