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.

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BACKGROUND: Iron (Fe) is essential for growth, but optimal intake is controversial. Our NICU practice was to supplement 2 mg/kg/d Fe for all preterm infants receiving human milk when they achieved full feeding volume. Adjusting Fe supplementation based on ferritin levels is thought to better address physiologic requirements. Our objective was to assess the impact of therapeutic monitoring of ferritin levels on the initiation and dosing of iron supplementation, hematocrit, transfusions, and oxygen radical diseases in preterm infants. METHODS: Preterm infants (<  32 weeks gestation, n = 100) were included. Ferritin was measured when full feeds were achieved, and then every 2 weeks. Fe was started at 2 mg/kg/d or continued at current dose for ferritin 40–300μg/L, increased by 1–2 mg/kg/d for <  40μg/L, or discontinued for >  300μg/L. Outcomes were compared with a historical control group. RESULTS: Ferritin levels were not predictable by dietary or transfusion histories. Using the ferritin protocol, 70% of infants received Fe at the time of full feeds, compared to 100% of controls. In contrast, all infants received Fe 4 weeks later, compared to 87% of controls. Mean age at Fe initiation increased (14.8±6.3 to 21.0±11.76 days). Peak doses were higher, with 32% receiving >  2 mg/kg day by 6 weeks, with fewer transfusions. The incidence of bronchopulmonary dysplasia and necrotizing enterocolitis did not change. CONCLUSION: An iron protocol based on ferritin levels results in later initiation, higher doses, and fewer transfusions, without increasing oxygen radical diseases.