Optimal nutrition is critical in the management of the ever-increasing number of surviving small premature infants. Although the most appropriate goal of nutrition of the low-birth-weight (LBW) infant is not definitively known, achieving a postnatal growth that approximates the in utero growth of a normal fetus at the same postconception age appears to be the most logical approach at present.1 In uncomplicated cases, growth will usually begin by the second week after birth, after the initial changes in body water distribution have taken place, and after the infant has accommodated in a nonstressful way to the provision of enteral feeds and parenteral supplements. The fetal standards of growth that will be considered here include not only weight and length, but also values for rate of retention of individual nutrients and minerals (Table 1).2 The quality of postnatal growth may differ from the quality of fetal growth, depending on the type of milk consumed, eg, ex utero weight gain of a premature infant given formula includes more fat gain than that of a fetus of the same maturity.3

CALORIC REQUIREMENT

Energy expenditure for maintenance and growth determines the caloric requirements of the infant. The energy expenditure for growth includes both the energy value of the new tissue and the energy cost of the tissue synthesis. The estimated "basal" or maintenance metabolic rate of LBW infants, including an irreducible amount of physical activity, is lower in the first week after birth than later, and in a thermoneutral environment is approximately 50 kcal/kg/d by 2 to 3 weeks of age.4,5

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