Donor milk is typically used for: - Babies born at less than 30 weeks  - Babies born weighing less than approximately 3 points and 5 ounces (1500 grams) - Babies whose sibling is receiving donor milk sibling because they meet these criteria 

Some mothers are unable to produce an adequate volume of breast milk for appropriate newborn feeding due to illness, stress, medication, or having had an operation for delivery.

Studies have found that overall, if a baby is unable to have their parent’s own milk, donor milk leads to better health outcomes than formula. Babies who receive donor human milk are less likely to need IV nutrition compared to babies who receive formula, and also have a lower risk of bowel complications.

Donated milk is pasteurized and tested with parent and baby safety at the core. Pasteurization of milk is a heating process that kills any harmful bacteria or viruses that may be in the milk. This process preserves most of the milk's nutrients, immune properties, and other healthy components.

There are multiple types of milk pasteurization. The most common form of breast milk pasteurization is known as Holder Pasteurization (HoP) which works by heating donated breast milk to 62.5°C (145°F) for half an hour, and then cooling it back down to room temperature. HoP is recommended in all international guidelines for donor breast milk.

While HoP is effective at removing harmful bacteria from breast milk, there are concerns HoP leading to a loss of some positive macronutrients (carbohydrates, fats, and proteins). Secretory IgA, lysozyme, and lactoferrin are all proteins that can offer immunity protection for newborn. Studies suggest that HoP can result in some level of loss of these proteins. 

One study found that HoP retained 72.3% of secretory IgA, 21.8% of lysozyme, and 39.4% of lactoferrin, indicating significant loss of these proteins, particularly for lysozyme and lactoferrin. Another study found that the mean amounts of lactoferrin and secretory IgA were significantly reduced by 66% and 25.9% in pasteurized breast milk compared to non-pasteurized breast milk. Some studies have also shown a reduction in fats in the milk.

However, some milk banks and health centers will add additional nutrients and calories into donated breast milk. In addition, research does not currently suggest that HoP has any significant reduction of mineral contents (such as zinc and copper), sugars, or the protein β-casein – all important for an infant’s development. 

Research also suggests that pasteurizing milk at slightly lower temperatures than HoP can help to retain more helpful proteins. For instance, one study found that when human milk was pasteurized at 57°C for 30 minutes, all three of the proteins mentioned above were retained at least 90%, and had removed 99.9% of all bacteria.

Overall, while there is evidence of macronutrient loss with pasteurization, research suggests that the benefits outweigh any cons, and that the majority of breast milk’s beneficial macronutrients are retained. There are also other methods of pasteurization that have better even retention of macronutrients that could be considered.

A parent’s own milk is the best food for babies and has been shown to lead to the best health outcomes. However, a parent’s own milk is not always an option for a variety of reasons. When that is the case, donor milk from other healthy lactating people is an option for some babies. 

Donor milk is typically stored in what is known as a milk bank: a service that collects, screens, processes, and dispenses breast milk donated by nursing parents who are not biologically related to the infant who receives the milk. Often milk banks are partnered with hospitals to provide breast milk to neonatal intensive care units (NICUs). Donors are screened to ensure they are healthy and are not paid for their donations. 

One bottle of donated breast milk typically comes from 3 to 4 donors and is pasteurized. Because the milk is coming from multiple individuals, it cannot be guaranteed that the nutrition content of the milk is the same for every bottle. For example: one bottle may have a higher amount of fat than another.

Getting pasteurized donor milk from a milk bank is the safest alternative for an infant who is unable to have their parent’s milk. Informal and unpasteurized milk sharing can come with health risks.