A recurrent problem in the NICU is “bandwagon-jumping”. An intervention with some preliminary positive data, and a possible physiologic rationale is widely adopted and made part of QI bundles with little or no reliable evidence that it is either effective or safe.

One such is the hype surrounding fresh mother’s milk. There are a small number of studies showing the following impacts. (references at the end)

1. A reduction in laboratory indices of antioxidant activity with freezing and with refrigeration, has been shown, with the longer duration of refrigeration having a greater impact, compared to never refrigerated milk.
2. An impact of pasteurization, but not freezing and thawing, on Leptin concentrations, but not Adiponectin or total protein
3. Freezing and thawing reduce glutathione content
4. No impact on total fat or carbohydrate of freeze/thawing, possible increase in Free Fatty Acids.
5. Freezing inactivates the majority of CMV, decreasing viral load, but does not eliminate entirely
6. Vitamin C concentrations are reduced by refrigeration and by freezing

The effects on cellular components of refrigeration and/or freeze thawing are unclear, which is unfortunate as I suppose this is the reason that people want to give “fresh” breast milk. My literature search for this post was unable to find much data on the impacts of freezing and thawing on the endogenous cellular components of breast milk. It has been reported that the viable proportion of white cells in milk after freeze/thawing is 78% or 19%. But exactly how to determine which type of white cell is still active, is unclear to me, the most recent report I found is a brief letter with little methodological detail, which determined viability with “propidium iodide” and measured some cell markers.

It looks however, like there is probably little effect on the bacterial components of breast milk. This study, Marin ML, et al. Cold storage of human milk: effect on its bacterial composition. J Pediatr Gastroenterol Nutr. 2009;49(3):343-8, for example, showed the same species and the same number of organisms in fresh and freeze/thawed milk.

And here another word of caution, what is meant by “fresh” isn’t always the same, sometimes it means never refrigerated, sometimes never frozen, sometimes not pasteurized. A recent statement from France, for example differentiates between “Raw” milk, meaning never refrigerated, and “Refrigerated” milk, with “Fresh” meaning either raw or refrigerated but never frozen. That working group developed guidelines to improve provision of raw milk, despite not presenting any clear reliable evidence of a clinical benefit.

Overall then, it seems that there is little adverse impact of freezing and thawing on macronutrients or cellular components of breast milk. There are some individual impacts, especially on vitamin C.

I guess the current enthusiasm for trying to give fresh milk must, therefore, be based on good clinical data of a benefit? (That is an ironic question, I already know the answer!) There is one cohort study (Huang J, et al. Short-term effects of fresh mother’s own milk in very preterm infants. Matern Child Nutr. 2023;19(1):e13430) comparing outcomes between babies who received “Fresh” mothers own milk, which was what the French group would call Raw milk (i.e. never refrigerated) and used within 3 hours, with the comparisons receiving pasteurized MoM. There were 170 babies <32 weeks GA in total, averaging 1150 g and 29 weeks. NEC and LOS were more frequent in the non-randomized control group, 16% and 19%, vs 10% and 7% in the controls, and there were some very small differences in feeding tolerance. The mother had to provide milk every 3 hours during the entire NICU stay.

Another Chinese cohort study (Sun H, et al. Testing the feasibility and safety of feeding preterm infants fresh mother’s own milk in the NICU: A pilot study. Sci Rep. 2019;9(1):941) compared a group of babies <30 weeks GA who received one feed a day of “Fresh” milk (unclear whether it was allowed to be refrigerated during the 4 hours that was permitted between expression and administration) to a group who received only frozen thawed milk. Infants received either MoM or donor milk (DHM), and it seems that some of the control babies could have received only DHM. There were close to 100 babies per group, averaging about 28.5 weeks gestation and some of the fresh milk babies dropped out and were not analyzed. The birth weights in the 2 groups are not mentioned, but they both, unusually, had a birthweight z score averaging about +0.3 (preterm infants usually average below 0). There was a very high rate of late onset sepsis (38%) and stage 2-3 NEC (14%) in the controls that was lower in the fresh milk group (22% and 6%).

One other study that I have seen quoted is a French database analysis which showed less BPD in NICUs that gave Fresh milk, but in that study the comparison NICUs gave pasteurized mother’s milk, as it was the recommended standard at that time in France. It also is not clear if the Fresh milk could have been frozen prior to administration or not. There was less BPD in the fresh NICUs, but no difference in NEC or in LOS, which was extremely frequent in both groups.

Although it seems attractive to some clinicians, there really is no reliable evidence that giving fresh breast milk, however it is defined, has different clinical outcomes, compared to frozen and thawed breast milk. Differences in composition are relatively minor, and impacts on cellular viability or numbers are really unclear.

The logistic implications, on the other hand, are substantial. Enabling the provision of an early fresh milk feed, daily fresh milk feeds, or exclusively fresh milk feeds, will require some resources, and organisation of those resources, to ensure that it could be done reliably and without errors in administration. A randomized controlled trial would be worthwhile to determine the true clinical impact, if any, of avoiding freeze/thawing of MoM, to see if dedicating those resources is worth it. One is planned and hopefully underway (Sun H, et al. A randomized controlled trial protocol comparing the feeds of fresh versus frozen mother’s own milk for preterm infants in the NICU. Trials. 2020;21(1):170), until the results are available, the potential benefits of Fresh, compared to Frozen and thawed, maternal breast milk must be considered Not Proven.

References (in chronologic order, most recent first)

Surmeli Onay O, et al. Evaluation of the Effect of Breast Milk Storage Conditions on the Viability of Cells in Breast Milk: A Pilot Study. Indian J Pediatr. 2024;91(10):1084.
Stinson LF, et al. Effects of Different Thawing and Warming Processes on Human Milk Composition. J Nutr. 2024;154(2):314-24.
Putri DK, et al. The Effects of Different Storage Conditions on Leukocytes in Human Breast Milk. Sultan Qaboos Univ Med J. 2024;24(1):91-8.
Binder C, et al. Human Milk Processing and Its Effect on Protein and Leptin Concentrations. Nutrients. 2023;15(2).
Edwards CA, et al. A systematic review of breast milk microbiota composition and the evidence for transfer to and colonisation of the infant gut. Beneficial microbes. 2022;13(5):365-82.
Volder C, et al. Transmission of cytomegalovirus in fresh and freeze-thawed mother’s own milk to very preterm infants: a cohort study. J Perinatol. 2021;41(8):1873-8.
Schwab C, et al. Characterization of the Cultivable Microbiota in Fresh and Stored Mature Human Breast Milk. Front Microbiol. 2019;10:2666.
Paduraru L, et al. Total antioxidant status in fresh and stored human milk from mothers of term and preterm neonates. Pediatr Neonatol. 2018;59(6):600-5.
Ahrabi AF, et al. Effects of Extended Freezer Storage on the Integrity of Human Milk. J Pediatr. 2016;177:140-3.
Handa D, et al. Do thawing and warming affect the integrity of human milk? J Perinatol. 2014;34(11):863-6.
Slutzah M, et al. Refrigerator storage of expressed human milk in the neonatal intensive care unit. J Pediatr. 2010;156(1):26-8.
Silvestre D, et al. Effect of pasteurization on the bactericidal capacity of human milk. J Hum Lact. 2008;24(4):371-6.
Hanna N, et al. Effect of storage on breast milk antioxidant activity. Arch Dis Child Fetal Neonatal Ed. 2004;89(6):F518-20.
Lawrence RA. Storage of human milk and the influence of procedures on immunological components of human milk. Acta Paediatr. 1999;88:14-8.
Jocson MAL, et al. The Effects of Nutrient Fortification and Varying Storage Conditions on Host Defense Properties of Human Milk. Pediatrics. 1997;100(2):240-3.
Williamson MT, Murti PK. Effects of Storage, Time, Temperature, and Composition of Containers on Biologic Components of Human Milk. J Hum Lact. 1996;12(1):31-5.
Friend BA, et al. The Effect of Processing and Storage on Key Enzymes, B Vitamins, and Lipids of Mature Human Milk I. Evaluation of Fresh Samples and Effects of Freezing and Frozen Storage. Pediatr Res. 1983;17(1):61-4.
Reynolds GJ, et al. A simplified system of human milk banking. Early Hum Dev. 1982;7(3):281-92.
Pittard WB, Bill K. Human Milk Banking: Effect of Refrigeration on Cellular Components. Clin Pediatr (Phila). 1981;20(1):31-3.

I ran out of energy in trying to add all the hyperlinks to the references, but I guess if you care you can easily find them, all available through PubMed.