Experimental study showed that adding fortifier and extra-hydrolysed proteins to preterm infant mothers' milk increased osmolality

Aim: Measuring milk osmolality after adjustable fortification is clinically relevant, as values exceeding recommended safety thresholds might result in gastrointestinal consequences. The aim of this study was to evaluate the effect of four fortification levels and storage time on the osmolality of human milk.

Methods: This was an experimental study using 71 spare samples of fresh breastmilk collected from 31 mothers of preterm infants. Osmolality was measured before and after adding commercial human milk fortifier containing dextrinomaltose and hydrolysed proteins at four different concentrations. Measurements were performed at various points during the 23 hours after fortification.

Results: The mean basal osmolality of the 71 human milk samples was 296 ± 14 milliosmoles (mOsm)/kg, and these remained stable over a period of 23 hours. Just after fortification, the four fortified formulas showed higher osmolalities than the nonfortified human milk, ranging between 384 ± 14 and 486 ± 15 mOsm/kg, respectively (p < 0.01). This osmolality increased significantly from 20 minutes to 23 hours after fortification (p < 0.05).

Conclusion: Adding fortifier and extra-hydrolysed proteins to human preterm milk increased osmolality, and these osmolality levels also increased with time. We recommend evaluating the risk of hyperosmolality when a higher fortification level is needed, to avoid gastrointestinal problems.