Influence of refrigeration or freezing on human milk macronutrients and energy content in early lactation: Results from a tertiary centre survey.

Background: Neonates with severe conditions that cannot be breastfed should receive fresh or preserved expressed human milk in addition to parenteral nutrition.

Objective: To identify the time during lactation when the macronutrients provide maximum energy and evaluate the effect of refrigeration and freezing.

Methods: We analyzed the composition of fresh milk, refrigerated at +4°C and frozen at -20°C, expressed by mothers of 60 preterm and 30 term infants from a level III maternity, in colostrum, transitional, and mature milk.

Results: In fresh milk, the protein level constantly decreases during lactation, with a significant difference after 3 weeks of lactation. Preterm milk of day 21 and day 30 had significantly lower protein than term milk (1.27 versus 1.43 g/dL, P=0.015 and 1.13 versus 1.28 g/dL, P=0.001). Refrigeration for 72 hours of term milk decreased protein content less than freezing. Preterm colostrum has significantly less protein after 48 hours of refrigeration or freezing. Preterm milk from day 60 lost carbohydrates if refrigerated 72 hours or frozen for 2 months. Lipids in preterm colostrum decrease after 8 weeks of freezing. Refrigeration for up to 72 hours did not change significantly the energy value of colostrum or transitional milk. Freezing preterm milk more than 2 weeks leads to significant loss of energy.

Conclusions: Milk frozen for more than 2 weeks contains less protein and energy than milk refrigerated for up to 72 hours. In the absence of milk bank access, in common settings, short-term refrigeration is preferable to long-term freezing.