Definition of Newborn jaundice:

Newborn jaundice is a condition marked by high levels of bilirubin in the blood. The increased bilirubin causes the infant's skin and whites of the eyes (sclera) to look yellow.

Causes, incidence, and risk factors:

Bilirubin is a yellow pigment that is created in the body during the normal recycling of old red blood cells. The liver helps break down bilirubin so that it can be removed from the body in the stool.

Before birth, the placenta -- the organ that nourishes the developing baby -- removes the bilirubin from the infant so that it can be processed by the mother's liver. Immediately after birth, the baby's own liver begins to take over the job, but this can take time. Therefore, bilirubin levels in an infant are normally a little higher after birth.

High levels of bilirubin in the body can cause the skin to look yellow. This is called jaundice.

Jaundice is present to some degree in most newborns, and is called "physiological jaundice." It usually appears between day 2 and 3, peaks between days 2 and 4, and clears by 2 weeks. Physiological jaundice usually causes no problems.

Other types of jaundice that usually cause no harm include:

• Breast milk jaundice is probably caused by factors in the breast milk that slow the rate at which the liver breaks down bilirubin. Such jaundice appears in some healthy, breastfed babies after day 7 of life, and usually peaks during weeks 2 and 3. It may last at low levels for a month or more.
• Breastfeeding jaundice is seen in breastfed babies in the first week of life, especially in babies who are not nursing often enough. Breastfeeding jaundice is different than breast milk jaundice.

Babies who are born too early (premature) are more likely to develop jaundice than full-term babies.

Conditions that increase the number of red blood cells that need to be broken down, and can cause more severe newborn jaundice:

• Abnormal blood cell shapes
• Blood type mismatch between the mother and the baby
• Bleeding underneath the scalp (cephalohematoma) caused by a difficult delivery
• Higher levels of red blood cells, which is more common in small-for-gestational-age babies and some twins
• Infection
• Lack (deficiency) of certain important enzymes

Conditions that make it harder for the baby's body to remove bilirubin may also lead to more severe jaundice:

• Certain medications
• Congenital infections, such as rubella, syphilis, and others
• Diseases that affect the liver or biliary tract, such as cystic fibrosis or hepatitis
• Hypoxia
• Infections (such as sepsis)
• Many different genetic or inherited disorders