All newborns should be screened for hyperbilirubinemia, whether the screening is clinical, transcutaneous, or blood sampling¹.

Breastfeeding infants tend to have higher physiologic total serum bilirubin levels compared to infants who are formula feeding². Studies indicate that 30-40% of breastfed infants have total serum bilirubin levels >5mg/dl at 3-4 weeks of age. There are 2 main reasons why breastfed infants have higher bilirubin levels:

1. Breastfeeding infants have a higher risk of excessive weight loss and lack of sufficient calories during the first week postpartum. This can be due to a delay in the milk coming in, infant feeding problems such as latch or sleepiness with lack of sufficient milk transfer, or maternal-infant separation leading to infrequent feeding. Lack of sufficient calories leads to higher levels of unconjugated bilirubin, at least partially due to increased intestinal reabsorption of bilirubin. Increasing calories with associated increased stooling helps to resolve the hyperbilirubinemia.
2. Breastmilk jaundice is a condition that starts as an exaggerated early physiologic jaundice in the first week. These infants continue with fairly high bilirubin levels for the next several weeks. The bilirubin level will gradually drift down over the course of 8-12 weeks. Suspected mechanisms include underlying Gilbert’s syndrome, with underactivity of the UGT1A1 enzyme responsible for glucuronidation of bilirubin³. Breastmilk is also known to suppress the UGT1A1 enzyme activity. Breastmilk jaundice has been observed to rapidly resolve by interrupting breastfeeding for 24 hours and feeding the infant cow’s milk-based formula. Formula is known to induce UGT1A1 activity. However, because the level of bilirubin in cases of breastmilk jaundice tends to be harmless, there is rarely a medical indication to interrupt breastfeeding.

Kernicterus is the most concerning outcome of hyperbilirubinemia¹. Infants at highest risk for kernicterus are late preterm infants who have insufficient breastfeeding skills, with excessive weight loss. Late preterm infants (35-37 weeks) have immature livers and weak blood brain barriers, allowing serum bilirubin to move more easily into extravascular spaces of the brain. Late premature infants who are not feeding well, especially if they have an ABO incompatibility or bruising, are at very significant risk for excessively high and dangerous bilirubin levels. Many hospitals have special feeding protocols for late preterm infants to help maintain proper hydration and assist mother with breastfeeding plans for this population. (See Late Preterm)

Early-term newborns, 37-38 6/7 weeks gestation, are also are at risk for insufficient feeding and have a greater risk of dangerous hyperbilirubinemia⁴, but are not typically included in hospital late-preterm feeding protocols.

The Academy of Breastfeeding Medicine’s protocol on management of hyperbilirubinemia in breastfeeding infants over 35 weeks gestation can be found at:

https://abm.memberclicks.net/assets/DOCUMENTS/PROTOCOLS/22-jaundice-protocol-english.pdf