Synopsis
Premature infants are a heterogeneous group with widely differing needs for nutrition and immune protection with risk of growth failure, developmental delays, necrotizing enterocolitis, and late-onset sepsis increasing with decreasing gestational age and birth weight. Human milk from women delivering prematurely has more protein and higher levels of many bioactive molecules compared to milk from women delivering at term. Human milk must be fortified for small premature infants to achieve adequate growth. Mother’s own milk improves growth and neurodevelopment and decreases the risk of necrotizing enterocolitis and late-onset sepsis and should therefore be the primary enteral diet of premature infants. Donor milk is a valuable resource for premature infants whose mothers are unable to provide an adequate supply of milk, but presents significant challenges including the need for pasteurization, nutritional and biochemical deficiencies and a limited supply.
Keywords: human milk, premature infant, necrotizing enterocolitis, donor milk, lactation
Introduction
Human milk provides the optimal nutrition for term infants. Human milk is also recommended for preterm infants, but does not alone provide optimal nutrition. The growth and neurodevelopmental needs of the evolutionarily new population of very premature infants are best met by appropriate fortification of human milk. To explore the role of human milk in the care of premature infants, it is appropriate to begin with a comparison of amniotic fluid (the optimal beverage of the fetus), milk from mothers delivering preterm, and milk from mothers delivering at term. We will then consider the benefits and challenges of providing human milk to premature infants, approaches to human milk fortification, the advantages and challenges of donor human milk products, and finally some practical approaches to increasing human milk consumption in premature infants.
In the United States, approximately 12% of infants are born preterm (prior to 37 weeks gestation).1 This is a very heterogeneous population with widely diverse nutritional requirements and highly different stages of immunocompetence. A 2.5 kg neonate born at 34 weeks gestation differs from a 500 gram neonate born at 24 weeks gestation in essentially every physiologic aspect of the gastrointestinal system and the innate and adaptive immune systems. Consequently the current body of knowledge about nutrition and host defense of premature infants has many gaps. Studies performed on larger older premature infants may not be applicable to the extremely low birth weight infants (ELBW, <1000 grams) that now survive routinely.
Amniotic fluid, “Premature” human milk, and “Term” human milk
Amniotic fluid contains amino acids, proteins, vitamins, minerals, hormones, and growth factors. While the concentration of these nutrients is much lower than that found in human milk, the large volumes of amniotic fluid swallowed in utero (up to a liter a day late in gestation, considerably more than the newborn consumes after birth) have a significant impact on growth and maturation of both the fetus and the fetal intestine.2 Animal studies and limited human observations suggest that swallowed amniotic fluid accounts for about 15% of fetal growth.3–5
Milk from women who deliver prematurely differs from that of women who deliver at term. Preterm milk is initially higher in protein, fat, free amino acids, and sodium, but over the first few weeks following delivery these levels decrease (Figure 1A). The mineral content (including trace minerals) of preterm milk is similar to that of term milk, with the following exceptions: calcium is significantly lower in preterm milk than term milk and does not appear to increase over time while copper and zinc content are both higher in preterm milk than term milk and decrease over the time of lactation.6, 7
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