Effects of Nutrition Supplementation on Osmolality of Expressed Human Milk.

Background: Provision of human milk to premature infants optimizes outcomes, but it must be supplemented to meet their nutrient and caloric requirements for growth. Our objective was to quantify the osmolality of human milk mixed with commercially available human milk fortifiers (HMF) and powdered infant formula, as currently fed to premature infants, simulating standard neonatal intensive care unit feeding practices for mixing and refrigerator storage.

Methods: Expressed human milk (EHM) samples obtained from mothers of premature infants (≤32 weeks gestation) were mixed with standard commercial products, and osmolalities were quantified.

Results: HMF significantly increased the micronutrient content and osmolality of EHM. Osmolalities were 291 ± 6 mOsm/kg (mean ± SD) for unsupplemented milk, and 505 ± 5 and 315 ± 19 mOsm/kg after supplementation to 24 kcal/oz using 2 current U.S. Liquid EHM fortifiers. When using powdered infant formulas to further increase the caloric content of fortified EHM >24 kcal/oz, osmolalities increased by 10.5-23.0 mOsm/kg for each additional kcal/oz. The use of powdered formulas alone (without HMF) increased osmolality without comparable increases in nutrient content. Refrigeration for 24 hours did not affect osmolalites.

Conclusion: Our finding that several common feeding formulations exceed 450 mOsm/kg, and the lack of evidence of adverse effect, raise the question of whether current maximum osmolality guidelines should be reevaluated to enable optimal nutrition for infants in neonatal intensive care.