Normally bilirubin passes through the liver and is excreted as bile through the intestines. Jaundice occurs when bilirubin builds up faster than a newborn's liver can break it down and pass it from the body. Reasons for this include:

• A newborn baby's still-developing liver may not yet be able to remove adequate bilirubin from the blood.
• More bilirubin is being made than the infant's liver can handle.
• Too large an amount of bilirubin is reabsorbed from the intestines before the baby gets rid of it in the stool.

High levels of bilirubin - usually above 20 mg - can cause deafness, cerebral palsy, or brain damage in some babies. In rare cases, jaundice may indicate the presence of hepatitis.

Types of Jaundice
There are several types of newborn jaundice. The following are the most common:

Physiological (normal) jaundice: occurring in more than 50% of newborns, this jaundice is due to the immaturity of the baby's liver, which leads to a slow processing of bilirubin. It generally appears at 2 to 4 days of age and disappears by 1 to 2 weeks of age.

Jaundice of prematurity: this occurs frequently in premature babies since they take longer to adjust to excreting bilirubin effectively.

Breast milk jaundice: in 1% to 2% of breastfed babies, jaundice can be caused by substances produced in their mother's breast milk that can cause the bilirubin level to rise above 20 mg. These substances can prevent the excretion of bilirubin through the intestines. It starts at 4 to 7 days and normally lasts from 3 to 10 weeks.

Blood group incompatibility (Rh or ABO problems): if a baby has a different blood type than the mother, the mother might produce antibodies that destroy the infant's red blood cells. This creates a sudden buildup of bilirubin in the baby's blood. Incompatibility jaundice usually begins during the first day of life. Rh problems once caused the most severe form of jaundice, but now can be prevented with an injection of Rh immune globulin to the mother within 72 hours after delivery, which prevents her from forming antibodies that might endanger any subsequent babies.

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