[Effect of adding fortifiers and protein supplements on the osmolality of donated maternal milk]

The fortification of maternal milk (MM) is a standard practice in order to achieve the requirements needed for the growth and development of the premature newborn. However, its osmolality could increase. According to the American Paediatrics Academy, it is recommended not to exceed 450 mOsm/kg (approximately 400 mOsm/L) in the diet of the infant, even though the safety limit is estimated to be between 400 and 600 mOsm/kg. The aim of this study is to determine the osmolality of thawed and fortified donated MM (DMM).

An analysis was performed on DMM of 6 healthy mothers, without fortifying, and with 4 levels of fortification. Measurement of the samples was carried out in triplicate at 0, 4, 9, and 24hours after their preparation. They were stored refrigerated (2-8°C) between measurements. The study groups were: (A) Non-fortified DMM; (B) DMM with vitamins added; (C) with the addition of a fortifier; (D) with the addition of a low-dose protein formula; and (E) with the addition of a high-dose protein formula. The osmolality determinations were carried out using a freezing-point osmometer. The data analysis was performed using R software (v.3.5.1).

A total of 30 samples were analysed with 360 measurements. The osmolality of the DMM at t=0h was 301 mOsm/kg (SD 5.2) and slightly increased with time to 308.11 mOsm/kg (SD 5.21) after 24hours (t=24h), being maintained within the safety limits. The addition of vitamins (Group B) did not significantly increase the osmolality. The addition of a fortifier (C) and a low dose (D) or high dose (E) protein formula produced an increase in the baseline osmolality that increased statistically significantly in time (P=.007), but with no differences between the C, D, and E types. There were differences between the osmolality at t=0 with the fortification according to the manufacturer's data sheet (339 mOsm/l) and the findings in our laboratory (432.33 mOsm/l).

The osmolality values found in the thawed DMM samples were similar to those of other studies. The fortification of the DMM samples and their storage refrigerated at 2-8°C for 24h increased the osmolality, but keeping them within the safety limits.