Composition of breast milk from mothers of preterm infants.

The influence of daily mechanical expression of breast milk on nutritional composition was examined by comparing expressed milk from 12 mothers who delivered preterm with milk from two groups of mothers delivering at term: nine mothers who mechanically expressed all milk and five mothers who nursed their infants at the breast. Collections were obtained at four-hour intervals over a period of 24 hours so that variability of constituents in milk of different mothers, as well as variability in the same mother over a 24-hour period, could be assessed. Preterm milk contained significantly higher concentrations of protein, sodium, and chloride, and lower concentrations of of lactose than the milk from either group of mothers delivering at term. The mean concentrations of protein, sodium, chloride, and potassium in early preterm milk were adequate to meet the estimated requirements for the preterm infant. However, there was large variability in nutritional composition of milk among mothers and among samples from the same mother.