Topic Outline
Topic Outline
Topic Outline


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:




  1. Academy of Breastfeeding Medicine Protocol Committee. ABM Clinical Protocol #22: Guidelines for Management of Jaundice in Breastfeeding Infants 35 Weeks or More of Gestation; Revised 2017 Breastfeeding Med 12(5) p. 250-257
  2. Maisels MJ, Clune S, Coleman K et al The Natural History of Jaundice in Predominantly Breastfed Infants Pediatrics 2014; 134:e340-e345
  3. Fujiwara R., Maruo Y., Chen S., Tukey RH. Role of extrahepatic UDP-glucuronosyltransferase 1A1: Advances in understanding breast milk-induced neonatal hyperbilirubinemia Toxicology and Applied Pharmacology 289 (2015) 124-132
  4. Academy of Breastfeeding Medicine. ABM Clinical PSrotocol #10: Breastfeeding the late preterm infant (34 0/7 to 36 6/7 Weeks Gestation) and Early Term Infants (37-38 6/7 Weeks Gestation) Second Revision 2016 Breastfeed Med. 2016; 11(10)