Macromineral balances in premature infants fed their own mothers' milk or formula.

The premature infant's own mother's milk (preterm milk) and modified infant formula (SMA, 67 and 80 kcal/dl) were fed to paired groups of seven infants, all of whom were of very low birth weight (VLBW) (less than 1.3 kg) and were studied during the first month of life. Sodium, potassium, magnesium, calcium, and phosphorus status was compared. The apparent retention of sodium from their mother's milk paralleled intrauterine retention rates and was greater than retention from SMA formula (P less than 0.01) during the first two weeks of life. However, when the formula was supplemented with NaHCO3 to intakes of 2.7 mmol Na/kg/24 hr after week 2, the infants retained adequate amounts of sodium. Potassium retention was similar to intrauterine retention rates in both groups throughout the four postnatal weeks. Magnesium intake, but not retention, was consistently higher in the group fed SMA (P less than 0.01), and intrauterine retention rates were achieved only in the group given formula. Calcium and phosphorus intakes from SMA were also higher (P less than 0.01) than from human milk. However, retention of calcium and phosphorus in both groups did not meet intrauterine retention rates, and hypophosphatemia developed in infants who received their mothers' milk. Growth in length and head circumference in both groups approximated intrauterine growth rates. If it is assumed that body composition of the growing VLBW infants should be similar to the composition of the fetus at corresponding gestational ages, then their nutrient requirements should be based on knowledge of intrauterine nutrient accretion rates. Based on this premise, we conclude that, for the growing VLBW infant, early maternal milk provided for sufficient retention of sodium, chloride, and potassium during the first four postnatal weeks. Neither human preterm milk nor SMA supplied adequate calcium and phosphorus for the growing VLBW infant.