Donor Milk Banking - Safety, Efficacy, New Methodologies

Abstract

Donor milk (DM) is of increasing interest as primary nutritional source for preterm infants. Safe access requires special infrastructure, trained staff, sophisticated algorithms, and stan-dard operating procedures as well as quality control measures. DM has limitations like low protein content and unpredictable composition of the other macronutrients, despite forti-fication frequently not meeting recommendations - both of them compromising growth. The first paragraph is devoted to COVID-19 and how it impacts processes of DM banking. The following paragraphs review aspects of “pasteurization,” “safety audits/donor screening,” and “DM nutrient variability.” In summary, (i) Holder pasteurization still is the most suitable procedure for milk banks, but high-pressure pasteurization or ultraviolet C irradiation conserve the unique properties of DM better and deserve more research to make it suitable for clinical routine. (ii) In regard to safety/screening, guidelines are valuable for safe DM bank operation, but they differ between legislations. There is a surprisingly high rate of non-dis- closed donor smoking (0.3%, p > 0.05) and of adulteration of delivered DM (up to 2%, p < 0.05) not detected by standard donor screening procedures. Frequencies differ between remunerated and non-remunerated programs. (iii) Neonatal caregivers should be aware of unpredictable composition of DM. They should be trained on how these can be overcome to avoid negative impact on growth and long-term outcomes like (a) measuring and disclosing nutrient contents of delivered DM batches to customers, (b) implementing certain types of donor pooling to reduce the risk of macronutrient depleted DM, (c) additional supplementation using 0.3-0.5 g protein/100 mL seems to be reasonable, (d) adjusted fortification may help to improve growth, but is not efficient in all preterm infants, (e) target fortification seems to improve growth (and probably also neurodevelopmental index) compared to standard fortification, (f) more research and clinical studies are needed. 

Introduction

Donor milk (DM) is of increasing interest as nutritional source for preterm infants, and on special occasions also for term infants. This interest is best reflected by a PubMed database search. For “donor milk,” 30 publications were listed in 2008 with an exponential increase to n = 205 in 2020 and an extrapolated n = 240 for 2021. One-quarter to one-third of these papers refer to “donor milk banking” as improving the process, technology, and quality is key to providing safe and efficient DM for this very vulnerable population. In this state-of-the-art review about safety, efficacy, and new methodologies of DM banking, we will discuss three topics, namely “pasteurization,” “donor screening,” and “nutrient variability of donor milk” in more detail.

Currently, we are facing a worldwide SARS-CoV-2 pandemic that has touched nearly all aspects of human life and societies, so we would like to take the opportunity to start by having a look into how COVID-19 has impacted the work of human milk banks.

SARS-CoV-2

Impact on Pregnancy and Human Milk

What do we know so far about the risk of virus transmission to the fetus/new- born? A number of studies gives us the picture that in utero vertical transmission remains unproven [1-4] and transmission of SARS-CoV-2 due to vaginal birth appears unlikely [1, 3, 5, 6]. With respect to postnatal exposition, experience with other respiratory viruses suggested that it is unlikely that SARS-CoV-2 is transmitted via breastmilk [7, 8]. And in fact, until the time being there is no evidence of viable, infective SARS-CoV-2 in human milk [7, 9, 10]. On the other hand, SARS-CoV-2-specific immunoglobulin has been found in breast milk of infected mothers which might have a protective effect for the newborn [7, 8, 11].

Already early in March 2020, low rates of serious illness in SARS-CoV-2 infants were suggested by the evidence [12-14]. Isolating infants from COVID mothers and prohibiting breastfeeding was not associated with less postpartum virus transmission than with permitted breastfeeding plus appropriate infection prevention and control measures [15]. WHO recommended that “...in infants, the risk of COVID-19 infection is low and the infection is typically mild or asymptomatic. However, the consequences of not breastfeeding or separation of mother and child can be significant.” [16]. As a consequence, WHO published detailed recommendations on 13 March 2020 on the care of mothers and infants when maternal COVID-19 disease is suspected or confirmed [17]. Recommendations were coded regarding (1) skin-to-skin contact, (2) early initiation of breastfeeding, (3) rooming-in, (4) direct breastfeeding, (5) provision of expressed breastmilk, (6) provision of DM, (7) wet nursing, (8) provision of breastmilk substitutes (BMS), (9) psychological support for separated mothers, and (10) psychological support for separated infants [16, 17]. In short, WHO recommended no change in practice in all of the above fields.

Impact of SARS-CoV-2 on Practical Human Milk Management

Real life, however, is quite different. A recent study compared national versus WHO recommendations in 33 countries across the globe including all World Bank economic country groups [18]. The authors found poor adherence to WHO COVID guidelines regarding mother-newborn care and breastfeeding or DM use. Especially, there was low adherence with respect to mother-infant proximity/rooming-in (only 33 and 36%), indicating some substantial COVID fear. There was poor recommendation of access to DM with suspected or confirmed maternal COVID (12 and 9%). Adherence to expressed breastmilk recommendation was significantly higher (73 and 70%). The degree of deviation from WHO recommendations was not correlated with infant mortality rates or World Bank classified economic power.

Besides not adhering to WHO recommendations, common pandemic control measures were identified as roadblocks for DM supply [19]. Deferral of donors for 28 days in case of COVID-19 history was common practice despite different evidence. A study by the “Virtual Communication Network” which was established to collect data and experiences from milk banks across 35 countries provided an illustrative narrative review in which seven pandemic-related vulnerabilities in service provision were identified [20], amongst them DM availability. On one hand, DM demand was reported to have increased, mostly because mother's own milk (MOM) was quarantined for babies from COVID+ mothers. Other sources reported decreased demand because there was lack of knowledge that SARS-CoV-2 is inactivated by pasteurization (apart from that other research found out that there is no transmission via human milk at all). With respect to supply, there were different reports about a DH shortage, for instance because outside-the-hospital donations were shut down to avoid overcrowding, because donor numbers decreased due to fear of leaving the house and trying to avoid hospital visits, because of difficult access to test centers and phlebotomy services for screening. Supply was also impacted because basic transport infrastructures closed (e.g., ferry network in British Columbia; some air freight services where milk banks serve large geographical area) but also again for milk quarantining (i.e., 14 days after pasteurization kept frozen and release only after reassurance by phone that donor mothers kept symptom-free for the previous 14-28 days). However, from other authors there were also reports that DM volume increased during COVID times - from 63 to 113 L/month [21]. This is supported by personal observations that the percentage of mothers increased who are successfully nursing MOM in-hospital. COVID social dis-tancing measures and in hospital visit restrictions seem to provide less distraction and disruption for mother-newborn pairs mostly because no one other than the father is granted access in most nursing units (pers. obs.).

SARS-CoV-2 and DM Supply

There are no detailed reports on how much SARS-CoV-2 impacted human milk bank functionality. Unpublished data from the DM bank from Leipzig, which is the largest one in Germany, indicate a two-step decrease in donations (by 40%) parallel to the lockdown activities (pers. commun. by Dr. Corinna Gebauer, Director of Donor Milk Bank, Leipzig). It is of interest to note that the demand for DM did not change despite reports that pandemic control measures might also reduce extreme prematurity (see Fig. 1).


In conclusion, SARS-CoV-2 should not affect DMB activities with respect to donor availability because it does not seem to be transmitted via human milk. However, pandemic control measures impact access to DM programs and pose a significant threat to the sustainability of DM supply.

Pasteurization: New Technology - Safety - Efficacy

The Role of Pasteurization

Pasteurization is a highly active research area in DMB operation. It involves new technologies and touches safety aspects of DM banking: pasteurization is needed to neutralize diverse germs (bacteria, virus, mostly Cytomegalovirus), and low-temperature long-time pasteurization also known as “Holder” is the most frequently used method. But it also involves aspects of efficacy: due to the energy applied to human milk, pasteurization can affect the integrity of valuable micronutrients, bio-factors, immunoglobulins, and cellular components that make human milk so unique [22-24]. It is common understanding that this cocktail should be preserved as much as possible. Though - on this occasion - it is of interest to note that for most of these factors, we currently do not exactly know what the biological meaning of these factors is. Do they play a specific role in preterm infants' gut health and growth or are they simply components of body fluids appearing in breast milk by transudation/passive transport/ultrafil- tration? Regardless of this discussion, the process of pasteurization is an indispensable step for DM safety, and the challenge therefore is to find the appropri-ate equilibrium between amount and quality of energies applied.

SARS-CoV-2 and Pasteurization

To continue with the SARS-CoV-2 theme, it is of interest to note that standard low-temperature long-time Holder pasteurization inactivates SARS-CoV-2, whereas cold storage down to -30 ° C and 48 h does not [25, 26]. It is also of interest to note that these studies used artificially SARS-CoV-2 spiked BM samples because the virus is not naturally found in human milk.

Comparison of Pasteurization Procedures

While Holder pasteurization currently is the method of choice, there are other procedures under investigation. Of interest are (i) high-temperature short-time pasteurization (HTST-P), (ii) high-pressure pasteurization (HP-P) and (iii) ul- traviolet-C irradiation (UV-C) pasteurization. While Holder uses 63 ° C for 35 min, HTST-P applies T >72 ° C for 15 s. HP-P uses pressures up to 500 MPsc (i.e., 5 X higher that the pressure present on the deepest point in the Pacific Ocean, the Mariana Trench) for several minutes at room temperature [27]. UV-C applies a wavelength between 200 and 280 nm for 10 to 50 s [28-30]. All methods eliminate bacteria and viruses, but conserve bio-factors to different degrees with HP-P and UV-C being the most promising ones (see Fig. 2) [31]. HTST-P and HP-P both need a special infrastructure, and the large-scale equipment requires a footprint that usually exceeds the capacity of most milk banks. Of interest to note that the research team of the milk bank in Warsaw (Poland) is developing a “miniaturized” HP-P device (U4000/86, Unipress, Warsaw, Poland) to reduce the burden on finances and space to make HP-P available for daily routine [32, 33]. A recent study confirmed that the combination of HP-P followed by freezedrying may be a future way to process donated HM and make storage less complicated because technically freezers would not be needed any longer [32]. An alternative method worth exploring is the UV-C method because of its simplicity, efficacy, and conservation of bio-factors.


In conclusion, Holder pasteurization is still the most suitable procedure for most milk banks, but HP-P and UV-C conserve the unique properties of DM better and deserve more research to make it suitable in clinical routine for all milk banks.

Other Safety Aspects

Standard Operating Procedures

Safe operation of a milk bank is key. However, there are no uniform rules that regulate the day-to-day business. Differences are found between international regulatory authorities (like within the EU), between countries, but also between states/provinces/cantons of the same country. Working groups and professional associations have tried to establish manuals and textbooks describing common knowledge [34-40]. Study of this literature is highly recommended to all institutions in charge of either already running a milk bank or of planning to establish one. In this context, we would like to draw the attention to the recent study of Ben T. Hartmann from Australia who published a very thorough review about benefits and safety issues of milk banks [41]. Fourteen chapters list the potential hazards for all procedures and for all parties involved as donors, recipients, units, processes, and comment by providing the appropriate references. This review should be part of the inventory of contemporary milk banks.

Extended Donor Screening

Current practice is to screen first-time donor mothers for transmissible diseases in a similar way as it is done by blood banks and to repeat in regular intervals. This incorporates a thorough medical history as well as some laboratory and microbiological tests. Standard milk banks usually do not extend their screening beyond this point. However, there is a risk that donors smoke, take other medication, or consume (illegal) drugs without disclosing it to the program. Other undisclosed donor practices that jeopardize the quality of donated milk and may put recipients at risk are (i) dilution of DM with water, (ii) addition of non-hu- man milk, or (iii) adding milk of a second donor. All these practices enhance the volume but deteriorate the quality and safety of DM and have been reported from programs that remunerate donors for the amount of delivered milk. But also in non-remunerated programs, it cannot be excluded that single donors follow such practice for a number of psychopathological reasons.

There is one paper that investigates the impact of extended donor screening, mainly by performing cotinine, medication, and drug tests, as well as tests to detect the presence of animal protein and of DNA other than from the registered donor's fingerprint [42]. The percentage of non-disclosed smoking was 0.3% and was not different between remunerated and non-remunerated programs (0.34 vs. 0.27%). There were no findings of illegal drug abuse or of other medication apart from 2 cases of oxycodone/oxymorphone in the non-remunerated program (9,439 samples tested) versus zero in the remunerated group (2,969 samples tested). The percentage of diluted samples, however, was significantly higher in remunerated donations (57 out of 2,875 samples tested, i.e. 2%) compared to 14 out of2,060 samples tested in the non-remunerated program (0.7%).

In conclusion, a number of guidelines and reviews provide valuable information about safe operation of DM banks, but they differ between legislations. In DM programs, there is a surprisingly high rate of non-disclosed donor smoking (0.3%) and of adulteration of delivered breast milk (up to 2%) not detected by standard donor screening procedures. It needs to be decided whether a cotinine- positive rate of 3 out of 1,000 samples justifies the call for extended screening. Milk adulteration occurs more frequently but would be safely identified once macronutrient content of DM is measured and disclosed on a routine basis (see the section below).

Efficacy of DM: Suggestions for Improvement

Nutritional Physiology and Human Milk

Human milk is considered as the best nutritional source for preterm infants because (I) of the protein quality provided, (II) it contains bifido-promoting oli-gosaccharides, and (III) of a plethora of bio-factors and cellular components (whose role for preterm gut health is not fully understood yet). The disadvantage of human milk, however, is the low content of protein (P) and energy (E) which does not allow growth at rates that are appropriate for preterm infants of up to 21-24 g/kg/day. Such growth rates require intakes of 3.5—4.5 g protein and 120— 160 kcal per kg and day — ideally in a balanced ratio of energy-to-protein (E:P). Comes on top that macronutrient levels vary within and between mothers and — what is even more important — the relationship between all macronutrients is highly variable as the mammary glands secrete carbohydrates, protein, and fat via different pathways. This means that there is no such thing as a more diluted or more concentrated human milk [43, 44]. In other words, human milk may provide all kinds of diets, balanced ones, but also diets with low-protein/high-fat or high-protein/low-fat or any other combinations that deviate from the optimum E:P ratio. Such unfavorable dietary intakes will jeopardize growth and potentially also neurodevelopment [45]. Unfortunately, no simple linear approach like increasing milk volume or standard fortifier strength above normal can correct “distorted” nutrient ratios and improve the efficacy of human milk. This is very nicely illustrated in a recent reply to letter to the Editor from our group (Fig. 3). As a consequence, concepts like target fortification (TFO) may be needed to overcome this significant problem [44, 46, 47].



DM and the Risk of Suboptimal Protein Supply

If preterm infants are fed DM, the risk of insufficient protein supply and postnatal growth faltering is even increased [48]. Protein content of DM is low because protein content drops during the first postnatal weeks to 0.8-1.4 g/100 mL, and DM is preferably obtained later in lactation [49]. Additionally, DM undergoes different handling steps like aliquoting, pasteurizing, freezing, thawing, and portioning to prepare daily feeds. The more frequently DM is handled the more macronutrients, especially fat (i.e., main determinant of energy), are lost to container walls [50]. There is an increasing number of publications that confirm this fundamental deficiency of DM and report deficits in functional, mostly neurodevelopmental outcome [21, 51-55]. In fact, a recent study from Tufts University in preterm infants fed either MOM, DM or preterm formula (PTF) found that the DM group had the lowest Bailey scores at 2 years of cor-rected age [52]. This group also grew poorly compared to the groups receiving MOM or PTF.

Improved neurodevelopmental outcome was also not found in the most recent and most comprehensive RCT on the effect of DM in preterm infants known as the DOMINO trial [53]. A total of 299 preterm infants was randomized to receive either DM or PTF in case of insufficient mother's own milk supply. Demographics were not different between both groups. There was a statistically significant difference in NEC cases. However, there was no difference in the 18 months Bailey neurodevelopment scores. Also, there were no differences in growth rates between both groups. These results are somewhat unexpected and disappointing. It can be speculated that the beneficial effects of DM NEC protection on neurodevelopmental index (NDI) are being cancelled out by a negative effect of DM. The following paragraph shall try to interpret these findings and find a potential explanation.

The absolute difference of 4.8% NEC rate (6.8% in PTF vs. 2.0% in DM) should translate into improved NDI. It is reasonable to assume that the average NDI of a NEC patient is approximately 25 points below a normally grown nonNEC preemie, so the DM group should have improved by 175 points, i.e. + 1.2 per subject. However, table 2 of the DOMINO trial report shows that the DM group is approximately -2 NDI points below the PTF group (depending on the scores assessed, range of -1.6 to -3.0). Assuming that this delta of -3 NDI points is solely caused by nutritional differences (mainly protein) - and taking Stephen's relationship of protein intake and NDI into account - the DM group must have received -0.36 g/kg/day of protein less compared to the PTF group [54]. This figure corresponds favorably to the difference of protein concentration between donor and average native mother's own milk. According to the review by Embleton and van den Akker [55] about protein intake and growth rates, this delta of -0.36 g protein/kg/day would translate into a difference in growth rate of -1.8 g/kg/day. The DOMINO trial, however, was not powered to detect such differences. In conclusion, less nutrient supply and poorer growth in the DM group could still be an explanation for not finding an NDI difference despite a 70% drop in NEC rate.

Improvement of Macronutrient Content of DM

There are different ways to improve the quality of DM. First and foremost, it would be helpful that DM banks disclose the nutritional content of each single batch they provide to neonatal units. Together with some education about nutritional physiology and growth NICU staff would be enabled to decide how ESPGHAN recommendations can be met with any given sample either by standard, adjusted, or target fortification, whatever would be the most appropriate and most simple approach to take. It is of interest to note that in a most recent paper by R. Lamb and coworkers from New Zealand it was stated that “...the variance in individual pooled DM indicates the importance of determining the nutrient composition of donated milk to inform fortification procedures.” [56]. Interestingly, DM banks in Poland measure macronutrient content using validated bedside methods and good clinical laboratory practice (GCLP) and disclose it to the unit (A. Wesolowska, pers. commun.) [57, 58].

Second, DM banks could start working on gradually reducing the variability of DM. This can be done by developing and evaluating pooling algorithms. A recent paper showed that multiple random pooling with up to 5 donors reduces the percentage of batches with critically low contents for both fat and protein. This can be improved by target pooling which requires prior knowledge of macronutrient content of all batches (i.e., best done by point-of-care analysis following GCLP [58]. These findings are confirmed by a study optimizing macronutrient content using different approaches and fortifiers [59].

A third approach would be to provide DM matched to gestational and postnatal age. The rationale is that protein content of human milk is high early in gestation and lactation - which to a certain extent parallels the requirements of preterm infants. There are some first clinical data on this concept available in a narrative review [21]. Protein content of DM can be as high as 2.1 g/100 mL which exceeds the average content of native human milk. With standard fortification adding some 1.1 g of protein per 100 mL, the ESPGHAN target of 3.0 g protein/100 mL could be reached. The study quotes better growth but does not provide detailed data. In summary, this approach looks promising. More clinical studies are needed. Needless to mention, this approach cannot fully compensate the risk of an unbalanced dietary E:P composition inherent in human milk either.

A fourth approach to improve macronutrient quantity and quality would be TFO. This concept acknowledges the fact of significant and unpredictable variability of macronutrient content of human milk. It attempts to correct imbalances by measuring macronutrient content of native breast milk batches, calculating potential deficits after standard fortification, and then adding appropriate modular nutrient components to reach ESPGHAN recommended intakes. TFO is not a super-fortification but identifies batches with insufficient nutrient content below standard assumptions and allows a more standardized macronutrient intake via breast milk. TFO is doable in clinical routine. The work to perform Donor Milk Banking - Safety, Efficacy, New Methodologies    67 measurements of milk is similar to bedside or point-of-care analysis of blood gas samples - a procedure that no neonatologist would question. And subsequent preparation of milk batches is not fundamentally different from adding standard fortifier. It has been shown that TFO improves growth rates, and there is also a trend towards improved neurological outcome (p = 0.07); however, due to the relatively small sample size, the statistical significance is not reached at the 5%, but at the 7% error level (PAS/SPR annual conference 2018).

In conclusion, feeding human DM to preterm infants reduces NEC rates and feeding intolerance. In return, however, dietary supply with macronutrients is unpredictable on a daily level and may cause postnatal growth restriction and impact neurological development. Neonatal caregivers should be aware of these drawbacks inherent in breast milk physiology and be trained on how these can be overcome. Understanding this context may improve somatic and neurode- velopmental outcomes.

Summary - Improvement of Quality and Efficacy of DM

-    Milk banks should measure the nutrient content of batches, improve pooling algorithms, and disclose the nutrient content of provided DM to the unit/ customer.
-    Certain types of donor pooling may help with avoiding macronutrient-depleted DM.
-    In the meantime, additional supplementation using 0.3-0.5 g protein/100 mL seems to be reasonable [60].
-    Adjusted fortification may help to improve growth, but is not efficient in all preterm infants. Data about NDI are not available.
-    Data from our double-blind RCT show that TFO improves growth compared
to standard fortification (most likely including NDI). It is precision medicine    
-    This is confirmed by other recently published trials.
-    More research and clinical studies are needed.

Conflict of Interest Statement

The authors declare no conflicts of interest. During the last three years, C.F. was invited as a speaker on conferences and/or had advisory roles with Medela, Nestlé, Hipp, Pro- lacta, Nutricia, Abbott, Hamilton. C.F. is a member of the executive committee of the Society of Neonatology and Pediatric Intensive Care (GNPI, Essen, Germany) and of the Human Donor Milk Bank Initiative (Frauenmilchbankinitiative, FMBI, Hamburg, Germany).

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