The effect of prematurity on milk composition and its physiological basis.

The composition of milk obtained from mothers giving birth prematurely is of current interest because of the use of this milk as a nutrient source for the premature infant. During the past 5 years research has established that the milk produced by mothers of infants of very low birth weight (e.g., 28-32 wk of gestation) is different from the milk of women giving birth at term. Preterm milk of early lactation is generally found to have higher levels of protein, nonprotein nitrogen, fat, energy, sodium, and chloride, but lower levels of lactose and greater interindividual variation. However, by the end of the first month of lactation the preterm mother's milk is very similar in nutrient composition to term milk, at least based on the incomplete information available at present. Many of the initial differences in composition of preterm compared with term milk may be explained provisionally from animal studies of mammary gland development. Possible explanations include reduced blood flow to the gland and hence milk volume, incomplete differentiation of mammary epithelial cells, and the absence of tight junctions between epithelial cells.