Providing optimal nutrition to a VLBW infant is difficult because there is no natural standard for comparison. For the healthy full-term infant, human milk is considered the “gold standard.” Human milk is used as the reference for the development of commercial infant formulas. While the milk of mothers who deliver their infants prematurely transiently has higher nitrogen, fatty acid content, sodium, chloride, magnesium, and iron, it is still inadequate for other nutrients, especially calcium and phosphorus. Therefore premature breast milk cannot be used as a standard for the development of premature infant formula. The special premature infant formulas use data from the accretion rates of various nutrients relative to the reference fetus, and from clinical studies of the development of the gastrointestinal tract which have defined the efficiency of absorption of nutrients and from metabolic studies.
The premature infant formulas are whey-predominant, which produces less metabolic acidosis than casein-predominant formulas in VLBW infants. The risk of lactobezoar formation is reduced when a whey-predominant formula is used. In addition, the concentration of protein per liter is approximately 50% greater than that of standard infant formula to provide three to four grams protein/kg per day (depending on volume fed). The fat is approximately 50% LCT and 50% MCT. The vitamin concentration is higher because the volume of formula consumed is significantly less in the VLBW infant. The calcium and phosphorus content is greater than standard formula, with some variation between formula manufacturers. The calcium-to-phosphorus ratio generally is 2:1 as compared to 1.4:1 to 1.5:1 with standard infant formulas.