How long do preemies need fortified breast milk?


Breast milk is the perfect, complete diet for newborn babies. But what about premature babies? The milk produced by the mother of a premature baby is gestation specific and therefore richer in the very nutrients that a premature baby needs more of for the first few weeks. But is this enough for the tiniest premature babies with very specific needs? This article looks at the nutritional needs of the smallest premature babies and the pros and cons of human milk fortifiers.

Support us on Social Media

Follow us on Facebook and Twitter

What premature babies need

Breast milk is by far the superior nutrition for premature babies. When premature babies are fed cows milk products they have poorer health outcomes and lower survival rates. However, some studies have indicated that the very lowest birth weight babies may need more of certain nutrients than breast milk can provide. For example additional calcium and phosphorus may be needed to prevent osteopeniabones with lower density and at risk of fractures, or supplements of vitamin D or iron may be needed 1 although the WHO states the evidence base for these supplements is weak2.Growth restriction or under-nutrition in tiny babies could be from placental insufficiency as well as inadequate nutrition after the birth. Whatever the cause, poor growthcould permanently affect ababys longterm health.3

Common practice

Common practice in many baby units is to supplement premature babies by adding extra minerals to mothers breast milk, usually in the form of cows milk based fortifiers calledhuman milk fortifiers. However the precise nutritional needs of the very premature baby, and the best way to provide them, are still under debate.45 Jack Newman, Canadian paediatrician and breastfeeding expert explains vitamin and mineral supplements can be suppliedas single preparations without using fortifiers:

Excerpt from

Breastfeeding the Premature Baby, Jack NewmanMD, 2017

There may be a need for additions to the breastmilk, depending on the babys levels in the blood. It is possible to add vitamin D, phosphorus, calcium, even human protein (albumin) and human milk fat (from a breastmilk bank) to the babys milk without using fortifiers. If the baby doesnt need fortifiers, then fortifiers actually should be considered diluters since they decrease the concentration of all those elements that make breastmilk special and unique.

How long do preemies need fortified breast milk?
Frozen breast milk

What are human milk fortifiers?

Human milk fortifiers (HMF) are commercially-produced, usually cow-milk-based, multi-nutrient fortifiers that supplement mothers breast milk intended for the smallest premature babies. Human milkfortifiers have varying amounts of protein, calcium, phosphate and carbohydrate, as well as vitamins and trace minerals. Eats on Feets explain:

Excerpt title

What about Fortifiers and Premature Babies? Eats on Feets, 2016

These fortifiers can be bovine-, soy- or human-milk based. Most HMF used in NICUs are bovine based. However, due to concerns with powdered formula and HMF, many NICUs use a mixture of liquid preterm formula or various commercial protein powders and minerals compounded in the hospital pharmacy.

Human-milk derived milk fortifiers are gradually becoming available.67First Steps Nutrition Trust describe more about a breast milk derived fortifier available in the UK from Prolacta and summarise studies comparing human milk based fortifier with cows milk based fortifiers.8

Not all preemiesneed fortifiers

Mathur et al 9found breast milk alone was enough for very low birthweight babies, particularly in the weight group 1251-1500g. And Sullivan et al 10 found extremely premature babies fed with an exclusively human milk-based diet had significantly lower rates of NEC (necrotising enterocolitis, see below) than a diet that included cows milk products .

Current guidance on use of fortifiers

Current guidance from the World Health Organisation (WHO) states:

Excerpt from

WHO Recommendations on Newborn Health, WHO, 2017

VLBW* [very low birthweight] infants who are fed mothers own milk or donor human milk need not be given bovine milk-based human-milk fortifier. VLBW infants who fail to gain weight despite adequate breast milk feeding should be given human-milk fortifiers, preferably those that are human milk based.

*Babies are termed Low Birth Weight (LBW) if they weigh less than 2,500g; Very Low Birth Weight (VLBW) if they weigh less than 1,500g and Extremely Low Birth Weight (ELBW) if they weigh less than 1000g.

First Steps Nutrition Trust is a charity which provides evidence-based and independent information and support for good nutrition from pre-conception to five years of age. They say:

Excerpt from

Human Milk Fortifiers. Information for health professionals. First Steps Nutrition Trust. Westland. 2020

Human milk fortifiers (HMF) are commonly used as a dietary supplement when babies are born prematurely, particularly among those born at under 33 weeks. For babies over 33 weeks gestation, breastmilk in sufficient volume (220ml/kg/day) is considered nutritionally adequate, although some vitamin and mineral supplements may be needed (Shaw, 2015).

The doctors in your babysNeonatal Infant Care Unit (NICU)will need to individually assess each babytaking account of availability of breast milk, your babys gestational age, and their medical needs.

Not enough breast milk?

Jack Newman, queries whether under-nutrition could be caused in part by false expectations of how a premature baby grows outside the womb and how often premature babies are fed:

Excerpt from

Dr. Jack Newmans Guide to Breastfeeding, Newman and Pitman, 2014

There is often great emphasis on making sure the baby gains weight at the rate he would if still in his mothers womb. But there is no proof that this rate of gain is necessary or even desirable. In fact, there are studies in the medical literature that suggest that too rapid a weight gain is harmful.

[Fortifiers] are intended to fix the deficiencies of breastmilk, but these deficiencies are, in large part, a function of how we feed premature babies. For example, the amounts we give them are very restricted much of the time. Prematures are often fed by the clock, typically every two or three hours. This is not normal for the baby born at term and I dont see why it would be appropriate for the baby born prematurely.

The need for fortifiers and preterm formulas disappears for some babies if we simply give them more breastmilk.

How do bovine milk fortifiers help growth?

Adding multi-nutrient fortifiers to breast milk is associated with short-term increases in weight, length and head growth.However by 12 months of age no differences were found between infants receiving fortified breast milk and those receiving unfortified breast milk.1112 Lucas et al also report on a study that showed breast milk fortifiers can help short-term growth when breast milk intake is high, but long term benefits were not proven.13

Do bovine milk fortifiers help health?

Whether or not health outcomes are improved by adding fortifiers can be difficult to establish because to do mass testing on vulnerable babies would be unethical. For each study citing benefits there seem to be many studies citing risks to the preterm babys health.

Risks of adding bovine based fortifiers to human milk

There are several known links between bovine fortifiers and serious health issues. Linda Palmer summarises:

Excerpt from

Fortify Human Milk for Premature Infants? from Baby Poop by Linda Palmer, 2015

it is well shown that feeding of cow products is also consistently associated with greatly increased chances of necrotizing enterocolitis, respiratory infections, other infections (sepsis), and other health risks including reduced survival. Re-hospitalizations are also more frequent in preterm infants who had been receiving formulas.The studies that have taken diet into account show greater developmental and intellectual benefits to fully human milk-fed preemies, as well as overall survival benefits, even though their weight gain is slower.

Fortification of breast milk with cows milk based fortifiers is associated with:

#1 Higher risk of gastrointestinal disease

  • More episodes of necrotizing enterocolitis (NEC) the most serious life-threatening gastrointestinal disorder that occurs for premature babies.14 15
  • More episodes of diarrhea and urinary tract infections with more antibiotic therapy.16
  • Increased osmolarity (concentration) of the feed can increase morbidity, risk of gastrointestinal disease including NEC, or bowel obstruction.17181920
  • More episodes of gastroesophageal reflux.21

#2 Higher risk of infection

  • Bovine fortifiers cancelsome anti-infective properties of human milk, eg lactoferrin, lysozyme, IgA specific to E coli.222324 Recent research showed a bovine fortifier reduced white blood cells by 76% and lipase activity (enzyme digesting fats) by 56% and a decrease in total protein.25
  • Bovine fortifier does not protect against infection by bacteria compared with human-milk derived fortifiers (Chan, 2007)
  • Bovine fortifiers increase the risk of contamination of breast milk becausepowdered fortifiers are not sterile, and liquid fortifiers dilute breast milks anti-infective properties.2627

#3 Higher risk of allergy and diabetes

  • Introducing cows milk protein to premature babies can increasetheir risk of allergy 28and diabetes mellitus29.
  • Artificial feeding is associated with increased gut permeability and decreased lactase activity (a marker of intestinal maturity).30


Particular issuesidentified with soy based formulas include low bioavailability of soy protein for low birth weightinfants, poor growth,low plasma levels of methionine, chloride and iodine, and high levels ofaluminium and phytoestrogen(WHO, 2006).

Mixing cows milk productswith human milk

Studies referencedabove by Chan et aland Quan et alfound that the cows milk protein in human milk fortifier and cows milkformula can prevent some of the important anti-infective properties in breastmilk from working. Rates of necrotizing enterocolitis were also significantly higher in infants fed mixed human and bovine-milk products compared to those fed breastmilk exclusively.

Where possible therecommendation is to give breast milk first rather than mixing breast milk with formula. If practical, waiting (20 minutes toone hour) before giving formula after breast milk allows time for breast milk to start to leave the stomach. When breast milk fortifiers are added to breast milk, First Steps Nutrition state:

Excerpt from

Human Milk Fortifiers. Information for health professionals. First Steps Nutrition Trust. Westland. 2020

It is currently advised that HMF be added to the minimum amount of breastmilk possible, and that this is used before fortifying any more milk to avoid prolonged storage, since the HMF may impact on the breastmilks immunological components (although this has yet to be quantified) (Shaw, 2015).

Helpingpreemie growth rates

  • Skin-to-skin contact andkangaroo care can significantly help a premature babys rate of growth.
  • Thecalories in breast milk can be increased by using breast milk cream, the fattier proportion of breastmilk, see Breastfeeding a Premature Baby.
  • Human milk derived milk fortifiers are gradually becoming available (Czank C et al, 2010)
  • Milk banks usually give priority topremature or sick babies should a mother be struggling with her milk supply. See organisations such as the Human Milk Banking Association of North America (HMBANA) or the European Milk Banking Association (EMBA)to locate a milk bank in your area. Human milk is far superior for these vulnerable babies.

Discussion documents and further reading

Various useful discussion documents for parents to find further information about human milk fortifiers include:

#1What about fortifiers and premature babies? Eats on Feets, 2011

A good review of research findings and who says what with the conclusion:

When it comes to adding fortifiers or other additives to breastmilk or not, there seem to be as many practices as there are NICUs. Controversy exists about many common and current practices.

#2 Fortify human milk for premature infants? Linda F Palmer, 2015

Author Linda Palmer comes to the conclusion that research on bovine fortifiers is poor:

Although current thinking is strongly in favor of fortifying human milk with additions of cow milk products, I am unable to find one study that shows human milk fortifiers provide survival benefits; reduced disability, such as blindness or cerebral palsy; or other neurological or health benefits. I find only studies showing increases in early growth along with increases in illnesses, with formula additions to breastmilk.

#3 Human milk fortifiers. Information for health professionals. First Steps Nutrition Trust. Westland. 2020

First Steps Nutrition Trust is a charity providing evidence-based and independent information and support for good nutrition. Their document linked above compares the nutritional content of commercial fortifiers.


There do not seem to be any easyanswers for parents of premature babies on the wisdomof adding bovine fortifiers to human milk, other than a general consensus that babies over a certain size do not need them. There seem to be many documented risks associated with the practice. Each baby will need special nutritional evaluation on a case by case basis by their Neonatal Intensive Care Unit (NICU). More research is needed.

Footnotes & References
  1. Optimal Feeding of Low-Birth-Weight Infants, World Health Organisation (WHO), 2006

  2. WHO Recommendations on Newborn Health, WHO, 2017

  3. The Nutritional Dilemma for Preterm Infants: How to Promote Neurocognitive Development and Linear Growth, but Reduce the Risk of Obesity, Brown and Hay, 2013

  4. Radmacher and Adamkin. Fortification of human milk for preterm infants. Seminars in Fetal & Neonatal Medicine. 2016

  5. Nutritional needs of premature infants: Current issues, Rigo and Senterre, 2006

  6. Design and characterization of a human milk product for the preterm infant, Czank et al, 2010

  7. Effectiveness of Human Milk-Based Fortifiers for Preventing Necrotizing Enterocolitis in Preterm Infants: Case Not Proven, Emblazon et al, 2013

  8. Human Milk Fortifiers. Information for health professionals. First Steps Nutrition Trust. Westland. 2020

  9. Physical growth and biochemical indicators of protein adequacy in exclusively breastfed neonates weighing less than 1500g, Mathur et al, 2000

  10. An exclusively human milk-based diet is associated with a lower rate of necrotizing enterocolitis than a diet of human milk and bovine milk-based products, Sullivan et al, 2010

  11. Brown et al. Multi-nutrient fortification of human milk for preterm infants, Cochrane Database of Systematic Reviews. 2016

  12. Multicomponent fortified human milk for promoting growth in preterm infants, Kuschel and Harding, 2004

  13. Randomized outcome trial of human milk fortification and developmental outcome in preterm infants, Lucas et al, 1999

  14. Current controversies in the understanding of necrotizing enterocolitis Part I, Noerr, 2003

  15. An exclusively human milk-based diet is associated with a lower rate of necrotizing enterocolitis than a diet of human milk and bovine milk-based products, Sullivan S et al, 2010

  16. The use of human milk for premature infants, Schanler, 2001

  17. Kreissl et al. Effect of fortifiers and additional protein on the osmolality of human milk: Is it still safe for the premature infant? Hepatology and Nutrition. 2013

  18. Effect of fortification on the osmolality of human milk, Janjindamai W et al, 2006

  19. Effect of fortification with human milk fortifier (HMF) and other fortifying agents on the osmolality of preterm breast milk, Agarwal R et al, 2004

  20. Milk curd obstruction in premature infants receiving fortified expressed breast milk, Wagener S et al, 2009

  21. Protein content and fortification of human milk influence gastroesophageal reflux in preterm infants, Aceti et al, 2009

  22. Effects of a human milk-derived human milk fortifier on the antibacterial actions of human milk, Chan GM et al, 2007

  23. The effect of nutritional additives on anti-infective factors in human milk, Quan R et al, 1994

  24. Effects of powdered human milk fortifiers on the antibacterial actions of human milk, Chan, 2003

  25. The effects of acidification on human milks cellular and nutritional content, Erickson et al, 2013

  26. Comparison of the Effect of Two Human Milk Fortifiers on Clinical Outcomes in Premature Infants, Thoene et al, 2014

  27. Optimal Feeding of Low-Birth-Weight Infants, WHO, 2006

  28. A prospective study of cows milk allergy in exclusively breast-fed infants,Host et al, 1988

  29. Prediabetes: prediction and prevention trials, Vendrame F et al, 2004

  30. Early feeding, feeding tolerance, and lactase activity in preterm infants, Shukman et al, 1998