Storage of Human Milk in NICUs

Abstract

Source: Slutzah M, Codipilly CN, Potak D, et al. Refrigerator storage of expressed human milk in the neonatal intensive care unit. J Pediatr. 2010; 156(1): 26– 28; doi: 10.1016/j.jpeds.2009.07.023Investigators from Schneider Children’s Hospital in New York investigated the safety of human milk refrigerated for up to 96 hours by analyzing bacterial counts and concentrations of lactoferrin, secretory (s)IgA, fat, fatty acids, protein, pH, and white blood cell count (WBC). Milk was collected by breast pump from mothers of infants in a neonatal intensive care unit (NICU), refrigerated at 4° C, and tested after 0, 24, 48, 72, and 96 hours.Milk from 36 mothers was obtained when their infants had a median age of 28 days. These neonates had been born at a median gestational age of 32 weeks. There were no significant changes in milk osmolality, sIgA, lactoferrin, total fat, total bacterial counts, or gram-negative colony counts in the milk over the 96 hours of refrigeration. Gram-positive bacteria colony counts declined significantly over the 96 hours. The WBC decreased by 16%, milk pH declined from 7.21 to 6.68, and total protein declined by 5% while free fatty acid concentration increased from 1.3% to 4.8% of total fat. There were no significant associations between gestational age, postpartum age, and other milk component measurements at baseline or with duration of storage.The authors conclude that human milk can be safely refrigerated for 96 hours without an increase in the bacterial cell counts or major change in the macronutrients and immune factors.As noted by the authors, guidelines on the safe storage of refrigerated breast milk have been limited by studies that have focused solely on bacterial colony counts and have not measured changes in other milk component concentrations. The current study was done in a NICU with a highly educated, middle class population, who may have been very careful in pumping and storing the milk under “very clean” conditions. It may not represent how the average mother expresses and stores her milk. Therefore, one should be careful in generalizing these results to other NICUs with different populations.One should be even more careful in applying the results of this study to mothers of infants at home, where cleanliness may be even less of a concern and refrigeration may not be ideal. Another issue, for mothers of full-term infants, is that this study was performed in mothers of premature infants. Premature breast milk possibly has more white blood cells and antibacterial activity than mature milk.1 Despite these caveats, the overall integrity of milk seems to be preserved for up to 96 hours of refrigerator storage.The physical and psychological benefits of breastfeeding for the infant, mother, and community need not be reiterated to AAP Grand Rounds readers. Breast milk is also recommended as optimal nutrition for premature infants. As previously reported in these pages (see AAP Grand Rounds, March 2002;7:292), however, both asymptomatic and symptomatic postnatal cytomegalovirus (CMV) infections have been transmitted by breast milk resulting in severe morbidity and mortality, especially among low-birth-weight infants.3 Although the authors of the present study assessed changes in bacterial counts after refrigeration, persistence of viral particles was not examined. CMV virions can remain infectious after prolonged storage at 4ºC.4 Freezing has been recommended, but there have been reports of CMV transmission to infants by their own mother’s frozen milk.5 Short-term pasteurization is an effective way to inactivate CMV found in breast milk. Similar studies in more diverse populations, examining the nutritional, immunologic, and infectious aspects of breast milk after varied modes of treatment could provide the data needed to determine optimal breast milk collection, handling, and storage practice.