Written by Dr. Steven McElroy, University of Iowa, and Dr. Misty Good, Washington University

I Gave My Baby Breast Milk. Why Did She Develop NEC?

As neonatologists who have dedicated their careers to understanding necrotizing enterocolitis (NEC), this is a question that we hear often, unfortunately. While we have learned much about NEC since it was first diagnosed decades ago, we still have a long way to go in understanding why NEC happens and how best to prevent and treat the disease. 

Nurses, doctors and parents are all frustrated by the lack of early warning signs. Too often, NEC develops suddenly, without warning to babies who seem to be stable and improving. Breast milk has been scientifically proven to help prevent NEC compared to infants who are fed formula. Yet, sometimes infants who are fed breast milk still get NEC, which can leave us confused and asking – Does breast milk actually prevent NEC? How? And, why doesn’t it always prevent NEC?

Does Breast milk prevent NEC?
The first human trial to look at the role of breast milk in preventing NEC was completed in 1990 by Lucas et al. In this study, the authors looked at 926 infants from 5 centers who had birthweights less than 1850g and randomized them to one of three groups: feeding breast milk only, feeding formula only, or feeding with a combined mixture of breast milk and formula. This paper showed that 7.2% of the infants fed only formula developed NEC, compared to 2.5% of infants who were fed a combination of formula and breast milk, and only 1.2% in infants fed exclusively human milk. While we know that breast milk helps to decrease NEC, it’s important to note that breast milk has not been shown to eliminate NEC. Source: https://www.sciencedirect.com/science/article/pii/0140673690933048?via%3Dihub

What about the kind of breast milk?
There are many reasons why some mothers may not be able to provide enough breast milk for their infants, so many NICUs use pasteurized donor milk instead of formula. A recent study on donor milk by Trang et al. published in Pediatrics randomized 363 infants to receive preterm formula or donor milk when mother’s milk was unavailable. In this study, infants fed pasteurized donor milk had a 3.9% NEC rate as compared to the 11% NEC rate in those infants fed formula. Source: http://pediatrics.aappublications.org/content/141/3/e20170737.long

What is in breast milk?
Breast milk is the ideal source of nutrition for nearly all infants. The composition of human milk changes during each feeding, varies over time as the infant grows, and varies from mother to mother. Factors such as ethnicity, diet, maternal age and health, and even time of day, can all influence the composition of human milk. Taken together, human milk is dynamic and adaptive. Breast milk is so much more than just a source of nutrition. Human milk has evolved over the millennia to nourish and protect infants who have underdeveloped immune systems. Breast milk contains biologically active proteins that can fight infection, provide immunity, and directly inhibit pathogenic microbial translocation and growth. Milk even contains its own bacteria that are believed to be helpful to the infant’s digestive tract and well-being.

Why doesn’t breast milk eliminate the risk of NEC?
Unfortunately, NEC is a complex disease, so it’s not as simple as giving breast milk and stopping all NEC. There are many other risk factors and variables to consider, including gestational age, prior instability or complications, antibiotic exposure and requirements, heart abnormalities, other intestinal disorders, and blood counts. How babies in the NICU are fed is important, too. Establishment of a feeding protocol has been shown to reduce the incidence of NEC in many NICUs. Source: http://pediatrics.aappublications.org/content/137/5/e20151119.long

What about the fortifiers?
Typically, breast milk alone doesn’t provide enough protein, minerals, or calories for the massive growth rate and bone development that a preemie undergoes. Growth is critical for the baby’s healthy development, and thus we supplement breast milk with fortifiers to provide essential nutrients. Practices and perspectives – in terms of how and what to fortify with – vary widely from center to center, and even from physician to physician. This topic demands its own dedicated blog post! Stay tuned!

In summary
For medically fragile babies, breast milk is like medicine. Breast milk – especially mother’s own milk – is critical to a baby’s healthy growth and development. Breast milk is known to protect against NEC and lower NEC rates. We are just beginning to understand precisely how breast milk provides protection. Once we gain this understanding, we will be one step closer to creating a world without NEC.