# Balancing Nutrition and Osmolality: Risk of Hyperosmolality During Individualized Fortification With Protein Fortifiers in an In Vitro Study

## TL;DR

This study examines how adding protein fortifiers to human milk for preterm infants affects osmolality, finding that careful selection of fortifiers is needed to avoid unsafe levels.

## Contribution

The study provides specific osmolality thresholds for different fortifiers, guiding safe fortification practices for preterm infants.

## Key findings

- Adding 1 g of preterm formula increased EBM osmolality to 384 mOsm/kg.
- MCF4 resulted in the highest osmolality (428 mOsm/kg) when added to fortified milk.
- Adding 1 g of protein fortifier exceeded safe osmolality thresholds with some MCFs but not others.

## Abstract

Background: Individualized fortification of human milk with protein fortifiers (PFs) and fat fortifiers (FFs) helps optimize the nutritional requirements of preterm infants but increases osmolality. This study aims to evaluate the impact of PFs and FFs on the osmolality of human milk fortified with multi-component fortifiers (MCFs).

Methods: The osmolality of 25 mL of expressed breast milk (EBM) was measured with six MCFs (1 g each), preterm formula (PTF), PF, and FF separately. Additionally, the osmolality of 25 mL of sterile water was measured with 1 g of each MCF separately. PF was added in increasing amounts (0.5, 1, 1.5, and 2 g) to fortified human milk (FHM), and the maximum amount of PF that could be added without exceeding the osmolality of 450 mOsm/kg was determined.

Results: The osmolality of EBM was 288 mOsm/kg, which increased to 384 mOsm/kg with the addition of 1 g of PTF. Among FHM, the highest osmolality was observed with MCF4 (428 mOsm/kg), and the lowest with MCF6 (327 mOsm/kg). The addition of 0.5 g of PF to FHM with MCF1 and MCF4 increased osmolality beyond the safe threshold but was within safe limits with MCF2, MCF3, MCF5, and MCF6. When 1 g of PF was added to FHM with MCF2 and MCF3, osmolality exceeded 450 mOsm/kg. However, osmolality remained within safe limits with the addition of 1.5 g of PF to FHM with MCF5 and MCF6. The addition of 1 g of FF did not alter the osmolality of EBM.

Conclusion: The addition of MCFs increases the osmolality of EBM, although within safe limits. However, as the addition of PF to FHM further raises the osmolality, it is essential to select the type of MCF and adjust the amount of PF to maintain osmolality within safe threshold limits.