What is known about human milk bank donors around the world: a systematic scoping review

Objective: The WHO recommends that low birth weight infants receive donor human milk (DHM) when mother’s milk is not available. Systematic reviews have been published regarding clinical outcomes of infants receiving DHM, as well as the impact of pasteurisation on the composition of DHM; however, information about milk bank donors has not been systematically assessed. Design: We conducted a systematic scoping review of original research articles about milk bank donors published before August 2020. Setting: Globally. Participants: Donors to milk banks. Results: A total of twenty-eight studies were included across a variety of geographies: the USA (n 8), Brazil (n 7), Spain (n 4), India (n 2), and single studies in France, Norway, Poland, Italy, Taiwan, Korea and China. Study variables were grouped into six main categories: Donor Demographics (n 19), Clinical Characteristics (n 20), Donor Experiences (n 16), Donation Patterns (n 16), Lifestyle Characteristics (n 4) and Lactation/Breast-feeding History (n 8). Some demographic characteristics were commonly reported across regions, while other, including gender and race, were infrequently explored. Factors that might influence the composition of DHM, including birth timing (term or pre-term), milk type (colostrum, transition or mature) and maternal diet were not regularly studied. Other gaps in the literature included (1) donors’ motivations and barriers to donation, (2) lactation and breast-feeding history, including factors that influence donors to pump and amass surplus milk, and (3) donation patterns, including whether donors are also selling milk to corporations or sharing milk with peers. Conclusion: What is known about milk bank donors in different geographies is often limited to a single study, with heterogeneity in the variables reported.

The WHO recommends that low birth weight infants receive donor human milk (DHM) when mother's own milk is not available due to evidence that it decrease the risk of necrotising enterocolitis (1,2) . Globally, DHM is typically produced by country-level milk banking networks that serve as a conduit between the recipient infants and the donors who provide the milk (3)(4)(5) . Although the recommended recipient for DHM is primarily the pre-term infant (2,6) , a recent review reported that DHM is also being used in other populations including healthy term infants and term infants with health risks. A 2020 report from a Virtual Communication Network of global milk banking leaders estimated that at least 800 000 infants receive DHM around the world annually (7,8) .
To ensure the quality and safety of DHM, human milk banks use similar hazard analysis and critical control points, where protocols are used in every step of the process, from donors screening until milk distribution (9) . Holder pasteurisation is the main processing technique used in milk banks, and although it inactivates virus such as HIV and cytomegalovirus, it also alters the milk composition (10) . A recent review found over forty studies that had evaluated the impact of Holder pasteurisation on DHM, suggesting that there is a growing body of knowledge about this technique (10) .
While there are multiple reviews on DHM recipients and milk banking processes, the donors to milk banks have not been systematically studied. A recent report by the WHO noted that 'the motivations behind donating human milk remain under-researched' (11) . Other information about milk bank donors may provide important insights regarding donor recruitment and the nutritional care of infants receiving DHM. For example, a donor's birth type (term v. pre-term) and milk type (colostrum, transition and mature) could influence the composition of the milk being collected by the milk banks (12) . Therefore, the aim of this review is to explore what is currently known about human milk bank donors globally and identify gaps for future research.

A systematic scoping review was conducted to investigate
what is known about milk bank donors. The objective of a scoping review is to map and summarise the information available for a research topic and to identify gaps where more research is needed (13) . The Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines were used to guide this review. The databases used to identify original research articles were PubMed and Scopus. Search terms utilised for both databases included 'Milk bank*' AND 'donors' NOT (composition OR pasteuri* OR nutri*). Additional studies were located by hand-reviewing bibliographies of the studies identified through the primary search.
Original research articles about milk bank donors that were published before August 2020 were included in this review. Studies were excluded if they were (1) about donor milk composition and/or pasteurisation only, (2) about infant feeding practices and/or infant nutrition only, (3) in languages that were not English, (4) not original articles or (5) not about milk bank donors (e.g. peer-milk sharing only). Two researchers (BGS and MTP) independently evaluated all study titles, abstracts, and full papers for exclusion or inclusion criteria, and differences were resolved after each review step by discussion.
Included studies were independently abstracted by two researchers (BGS and MTP) into a Microsoft Excel spreadsheet for the following information: study location, study design, study population, study objectives, data collection methods, variables related to milk bank donors, results and funding source. Studies that used multiple years of milk bank donor data were classified as semi-longitudinal study design, since some donors may have appeared more than once in data that spanned several years. Abstracted data were reviewed by two researchers (BGS and MTP) and discrepancies were resolved by discussion. Demographic data from one study combined donor and non-donor information and could not be interpreted; therefore, these demographic data were not reported in the results.
To organise study variables, an iterative process was used by two researchers working together to develop and refine a classification system of main categories and sub-categories for study variables. Categories and subcategories used to classify variables included (1) (14) , and Donation Duration.
The primary source of bias considered was selection bias, if donors included in a study were potentially not representative of the broader donor population. Studies were identified as possibly having selection bias if they did not discuss participant selection, had low participation rate (below 60 %) (15) or included a limited sampling frame (e.g. only bereaved donors, only donors active on social media). Selection bias was evaluated independently by two researchers and discrepancies were resolved by discussion.

Results
A total of 181 studies were identified through Scopus, 84 through PubMed and 8 through hand-review of bibliographies ( Fig. 1). After excluding duplicates (n 70), a total of 203 studies were screened. After a review of abstracts and titles, 154 articles were excluded leaving 49 articles for full-text review. Twenty-one studies were excluded after full-text review leaving twenty-eight studies in this scoping review about human milk bank donors  .
Studies in this systematic review were published between 2003 and 2020 (Table 1) and included 2 to 4000 donors. Eight studies were conducted in the USA, seven in Brazil, four in Spain, two in India, and individual studies were conducted in France, Norway, Poland, Italy, Taiwan, Korea and China. A qualitative design was used in eight studies, which allows for rich exploration of the donors' lived experiences. Qualitative studies were predominantly conducted in the USA and had a small sample size (2-21 donors and 80-107 online testimonials or images). Data collection methods used in the studies included interviews, questionnaires, chart reviews and online content analysis. In most of the studies, donors were recruited from a single milk bank (n 16). Ten studies (36 %) presented possible selection bias (  Table 4), (4) Lactation/Breast-feeding Experiences (n 8; Table 5), (5) Donor Experiences (n 16; Table 6) and (6) Donation Patterns (n 16; Table 7).

Discussion
Despite reports that there are now over 600 milk banks operating around the world (44) , and over 800 000 infants annually who receive DHM (7) , studies about milk bank donors are often limited to a single study per geography with significant heterogeneity in the variables reported.

Donor demographics
Age was the most commonly reported demographic variable, with some initial geographic differences observed. Specifically, donors were predominantly in their early-to mid-twenties in Brazil and India (based on mean donor age or prevalence of donors by age group) (20,21,23,32,34,42) , while donors were predominantly in their early-thirties in France, Korea, Norway, Poland, Spain, Taiwan and the USA (16)(17)(18)25,(27)(28)(29)(30)(31)33) . There were also geographic differences in education levels among donors, with studies conducted in Brazil reporting that the majority of donors were not college-educated compared to mostly college-educated donors in China, Norway, Spain, Taiwan and the USA (17,19,20,23,25,25,30,39) . Across all geographies, donors were predominantly married or living with a partner (16,(18)(19)(20)30,32,36) . Limited information was available on race-ethnicity (18,23,36) . No information was collected about gender in any of the studies, suggesting that donor gender may have been assumed in prior research. While this scoping   review identified some differences in donor demographics across geographies, interpretation of this information requires more context related to the local setting.

Donor clinical characteristics
Birth history frequently included a donor's number of children. Results varied by geographies, with some studies reporting that donors were predominantly primiparous and others predominantly multiparous (16-20,23,25,27-30, 32-36,38,39,42) . The percentage of donors that had preterm births were in the minority in most studies (8-24 %) (25,(27)(28)(29)33,39) , though two studies in India and Brazil reported the approximately half of donors gave birth pre-term (19,42) . Donor birth term could influence the composition of some nutrients in donor milk if donations are made in the first weeks postpartum (45,46) , suggesting that this may be useful donor data to regularly collect. Information regarding donors' diseases/conditions (22,33,34) and prenatal clinical care was limited (20,32) . Data on characteristics of the donor's child beyond birth term were also scarce. For example, no studies reported the sex of the donor's infant, and only a few studies reported hospitalisation status.

Lactation and breast-feeding experience
Donors reported similar beliefs about the importance of breast-feeding and breast milk across three geographies (26,30,32) . Donors' beliefs in the value of their milk was only explored in one study, with many donors expressing the desire for compensation. Information about donors' breast-feeding history, clinical support for lactation and milk expression practices was limited to one or two studies, suggesting this is an important area for future research to better understand the donor's path to having excess milk for donation.

2680 donors
The internet was the most popular source of information regarding donations (33 %) France (16)

7 donors
Major themes: information received about milk banks and perceived approval of family and friends, having excess milk, altruism, empathy, support from family and milk bank USA (18) 2007 87 donors To help others, having excess milk (% not provided) USA (24) 2012 21 donors Major themes: physical and emotional meanings of pumping, finding meaning in perinatal loss, and importance of healthcare providers addressing lactation with bereaved mothers USA (26) 2013 19 donors Major theme: deriving value from the physical and emotional labour of pumping USA (36) 2018 12 donors Major themes: hope of donation helping others, act of donating was nurturing for the donor, importance of support from healthcare staff and desire to share their stories USA (37) 2018 2 donors Major themes: milk donation as a mean of processing perinatal loss and doing something helpful with their milk USA (43) 2020 95 donor testimonials Major theme: having excess milk Barriers for donation Brazil (20) 2009 36 donors Main reasons to cease donation included returning to work and reduction in milk production Brazil (32) 2016 12 donors Major theme: limited information provided prenatally Spain (30)

7 donors
Major themes: lack of healthcare provider knowledge, distance from milk bank, no support at work and decrease of milk production USA (18) 2007 87 donors Finding time to pump, transporting milk to the bank and problems getting blood test (% not provided) USA (37) 2018 2 donors Major theme: frequent pumping was difficult Donor identity USA (24) 2012 21 donors Major themes: identifying as a bereaved mother/grieving the loss of motherhood USA (40) 2019 80 donors Major themes: a temporal donor identity allowed bereaved mothers opportunity to process loss and reconstruct maternal/female identity USA (43) 2020 95 donor testimonials Major themes: donors had complex and fluid identity including being a woman, a mother, healthcare professional and prior recipient of milk donation

Donation patterns
There was a wide range of reported donation volumes per donor (mean or median 0·64-30 l and range 0·04-174 l) (17,18,25,28,31,33,38,39,41,42) . The wide range could be attributed to the differences in milk banking requirements. For example, in Brazil, there is not a minimum donation volume (47) , while in the USA some milk banks require a minimum donation of 100 ounces (48) . In India and Spain, donors with infants in the NICU/hospitalised provided significantly higher volumes than donors without hospitalised infants (28,42) . Donor type was mostly first time (v. repeat) in all regions, although it was not widely reported (16,20,25,31,32) . The type of milk commonly donated was mature milk, as the donations started mostly after 1 month postpartum (17,20,25,27,28,31,33,39) . This suggests that donors are frequently providing milk that is likely lower in protein than the colostrum and transition milk that would normally be provided by an infant's own mother in the early postpartum period. There was limited information about donation duration (range 2 weeks to 13 months) (17,20,33,37) . No studies collected information regarding whether milk bank donors provided their milk elsewhere, including either selling it or sharing with a peer.
donations were frequently reported, enablers and barriers for donation differ among regions studied and not enough is known about what motivates donors to donate. Additionally, factors that could influence the nutritional profile of DHM, including birth timing (term or pre-term), type of milk donated (colostrum, transition or mature), donor diet and infant characteristics, should be more frequently collected. Other factors that have not been widely studied included donor lactation and breast-feeding history, including factors that influence why donors are pumping and amassing surplus milk and donation patterns, including whether milk bank donors are also selling milk to corporations or sharing milk with peers.