What are preterm formulae and why are they important?

Preterm formulae are nutrient enriched to achieve rates of growth and storage deposition which ordinarily would have occurred in utero. They are therefore higher in protein, energy, minerals and trace elements.

Over the years infant formula manufacturers have sought to improve their products by conducting research on the efficacy and safety of adding specific bioactive ingredients. These ingredients were initially available in term formulae but are now widely available in the preterm and other specialised formulae currently available.

These small additions are thought to impact on various aspects of nutrition, growth and neuro-development. They include long chain polyunsaturated fatty acids, nucleotides and oligosaccharides to name a few. Research continues to show benefits to the infant with these additions.

How do the nutritional needs of preterm babies differ from term infants?
A premature baby is one born before the completion of 37 full weeks gestation. We are currently able to care for infants who are technically on the edge of viability being born at 23 and 24 weeks gestation. These infants can weigh little more than 500 grams and if one considers a term infant may triple its birth weight in its first year of life then these tiny premature infants often increase their birth weight some 15 to 20 times in the first year. This is phenomenal growth and development to undergo and it is hardly surprising that many of these infants previously ran into nutritional difficulties.

Almost all infants born before 34 weeks gestation will have little or no stores laid down and therefore all are technically deficient in minerals and nutrients and have no reserves to call upon.

For a preterm infant to grow they will need extra fat, carbohydrate and protein as well as minerals and electrolytes to grow adequately. In addition many of the infants will have an even greater need for energy to allow for the increased work of breathing, repair of tissues as well as brain growth and development.

The problems of infections in these vulnerable infants are also ever present and this will also add to the energy requirements to help them combat these adverse situations when they arise.

What preterm formulae are available?
The main preterm formulae available are of two distinct types. One is a very low birth weight formula suitable for nearly all infants less than 1800 grams. It has a standard casein to whey ratio and the calorific value is increased from a standard formula at about 68 kilocalories per 100mls to approximately 84 kilocalories per 100mls.

This is in the form of protein, fat and carbohydrate. In addition there is higher iron content as well as an increased sodium, potassium, calcium, and phosphate to address the immaturely functioning kidney and aid general and bone growth as well as mineralisation.

Osmalality of these formulae can be a factor as not all premature infants can tolerate preterm milk. Over the years the osmalality has come closer to breastmilk values overcoming these concerns.

The Tsang guidelines for infant nutrition were revised in 2005 mainly to address the nutrient needs of preterm infants. Preterm formulae are now based on these recommendations and the formulation is designed to give these vulnerable infants the complete nutrition that they require. Breastmilk is virtually always the preferered milk in any situation

At approximately 1800 grams in weight a nutrient enriched formula is often used as these have a slightly reduced calorific content from the very low birth weight formula to approximately 76 kilocalories per 100mls.

These formulae also have increased energy in the form of carbohydrate protein and fat as well as the increase in electrolyte and nutrient content.

The evidence suggests that even in these extremely preterm infants the sooner the milk is added to the immature gut then the less likelihood is there of gastrointestinal complications. When feeding is commenced and breastmilk is not available it will be explained to a parent that a preterm formula is recommended to be introduced to the immature gut.

The sooner the gut is primed with milk then the milk will be better tolerated as volumes are increased. Initially, however, the volumes used will have little impact on nutrition but more impact on the enzymic and hormonal aspects of the immature gut.

Some mothers are unfortunately unable to produce breastmilk in the required quantities or are sometimes unable to produce breastmilk at all. Some areas will have access to banked breastmilk but when these are not available the preterm formulae are the formulae of choice for the developing gut.

Should breastmilk or bank breastmilk be available then due to the lower calorific content of breastmilk either higher volumes are required to enable adequate growth or the addition of breastmilk fortifier is needed. These contain extra calories minerals and electrolytes to raise the levels in the supplied breastmilk as recommended by Tsang.

Preterm formulae of course do not have to be used exclusively and can be used in combination with breastmilk as and when it can be supplied.

Parents are of course a vital factor in infant nutrition and many parents come with little or no knowledge of prematurity and the differences that there are in these vulnerable infants. Talking to parents about feeding and the types of feed that are available are an integral part of the care that is required and parents need to be involved and educated about the choices that are available to them.


Many parents nowadays used the internet as a source of information and although we are all aware that information can be of variable quality we are able to direct them to sites which can help inform them about the types of milks and how feeding differs in the preterm infant.

Unfortunately a number of infants will require surgery on the gut and this can impact on the type of feeding that is able to be tolerated. Not only are there preterm specialised formulae available but there are also other formulae which are designed to help the problems of tolerance and absorption in those infants with a compromised bowel.

A relatively common type of specialised formula for these conditions would be a hydrolysed formula. This is where the protein molecules are broken down to smaller peptides and amino acids to enable easier digestion in the gut.

Fat formulation can also be altered by decreasing the ratio of long chain polyunsaturates to an increase in the medium chain triglycerides which also will aid fat absorption. Most formula milks are lactose based and although primary lactose intolerance is not very common in the western world, many specialised formulae are glucose based to avoid any potential problems. A far more common problem seen would be one of ‘cows` milk protein’ intolerance and a hydrolysed formula will also address this issue.

Outcomes for the preterm infant
Debates continue on nutritional issues in the preterm infant mainly surrounding the longer term outcomes. There are some who would consider the fact that formula fed infants gain more weight over the initial months than breastfed infants and whether or not this has a detrimental impact on future health, such as the development of cardiovascular disease or type 2 diabetes.

There is no doubt that it is very hard to get preterm infants to grow adequately in the first few weeks of life. Data analysis continues to show very poor weight gain and often substantial weight loss. There are studies looking at how more energy can be administered to the preterm infant early in life although practically this involves intravenous feeding.

The WHO has recently released new growth charts for the breastfed infant as the weight gain in these infants is usually less rapid then those who are formula fed. The confusion about this has led to concerns that breastfed infants on standard growth charts can be seen to be growing poorly and hopefully the new charts will address this issue.

Sometimes an infant’s gut is simply unable to tolerate milk for some months or weeks due to underlying conditions or post surgery. In these circumstances we have to feed these infants intravenously. In the long term one would hope to get all infants feeding enterally prior to discharge home.

More recent studies have been involving the growth restricted infant. In utero these infants have had poor nutritional and blood supply from the placenta and the gut is often severely compromised and can be intolerant of milk or milk products in large volumes. Studies have looked at how to best introduce feeds to these growth restricted infants and the best timing for the first administration of milk into the gut.

Current evidence would strongly suggest that the gut be primed with milk as soon as is practical. Preferentially this would be breastmilk or banked human breastmilk. When these are not available the evidence is also to introduce formula milk into the gut in a timely fashion.

In summary, one can regard the extremely preterm infant weighing less than 1000 grams as a nutritional emergency and certainly less preterm infants as a nutritional challenge. Despite our practices of commencing parental nutrition as soon as is practical in the first day or so of life and also administrating small amounts of milk to the gut in the form of a trophic feed, our extremely low birth weight infants would lose 10 to 15 percent of their birth weight and not regain this for some 2 to 3 weeks. It can take up to a month for us to achieve satisfactory weight increases in these infants and this is an area we still need to improve upon. The growth restricted infants are also a group who need to attain or achieve catch up growth. There is evidence that these and the preterm infants, due to having a poor nutritional intake, can develop future health concerns related to poor feeding and nutrition. This includes neuro development which can have a long lasting impact on the family.

It is not just the preterm and the growth restricted infant that require specialised formulae but those infants who have undergone surgery or indeed have unfortunately been born or developed conditions that interfere with milk tolerance as well as subsequent growth and development. The types of formulae available to us over the years have increased and the formulations have been improved upon and studied in great detail to maximise the benefit to the growing infant. Breastmilk will always be our first choice of milk in almost any situation that arises; however, the specialised formulae that have been developed to help these vulnerable infants have greatly contributed to the health and well being of the vulnerable.

Types of formulae
Standard term formulae are nutritionaly complete and suitable for almost all term infants from birth. They are usually indicated when breastfeeding is not possible or desired and will contain as do most of the formulae, prebiotics, nucleotides , LCP’s and added anti oxidants to ensure the best growth and development achievable. Although these formulae are suitable for infants for the first 12 months of life there are infant formulae available such as follow on or step up milks that can be used from the age of 6 months. These milks are formulated differently with an increased protein and carbohydrate content, less fat and a higher iron content. These formulae are particularly suitable for infants at risk of iron deficiency such as those being weaned onto a strict vegetarian diet and can be used up to 24 months of age.

Specialised formulae are also available from the age of 12 months onwards which like the follow on milks are not a breastmilk substitute but can be used as a good source of nutrition and are nutritionally superior to cows’ milk. Organic milks are also available from 6 months of age although these tend to be more of a lifestyle choice then a nutritional requirement. Certain nutritional additives are currently not available in organic form and therefore these milks are not as close to breastmilk composition as most non organic formulae. Soya based milks are also available although not usually recommended below 6 months of age due to phyto-oestrogen content. They therefore are suitable for infants from the age of 6 months and can be used in certain rare conditions such as galactosaemia and lactose intolerance.

Those wishing to follow a vegan lifestyle, although not recommended in the growing and developing child, would normally choose this milk if breastfeeding was not possible.

Hydrolysed formulae are available and ordinarily these would be used for the very relatively common condition of cows’ milk protein intolerance, however, this often mislabelled or misdiagnosed as lactose intolerance. Hydrolysed formulae can be used from birth and are nutritionally complete. They are often used in association and with specialised weaning diets usually with the advice of a dietitian.

Preterm formulae for the very low birth weight infant mentioned previously are an ideal substitute for those infants not able to receive breastmilk and suitable from birth to approximately 1800 grams in weight. After this time a nutrient enriched formula is often substituted and indeed infants may well be discharged on this formula into the community for the first three to six months of life. All preterm formulae are nutritionally complete and have good sources of iron, calcium and phosphorus. In some resistant cases of cows’ milk protein intolerance, rather than a hydrolysed formula, sometimes an elemental formula is required where the proteins are not simply broken down into peptides but broken down further to their amino acid bases. This type of feed is also sometimes necessary for those children who have had a large part of their intestines removed or are recovering from gastrointestinal surgery.

Finally although breastmilk is clearly what we would ordinarily wish to feed our new born infants, the premature infant may not receive enough nutrition energy from breastmilk alone. Breastmilk fortifiers are therefore available in the form of a powder which can be added to breastmilk to increase the energy, protein, vitamin, mineral and salt content required by the growing premature infant. These fortifiers once again are used approximately up until a weight of 1800 grams and sometimes beyond and then can be removed from the breastmilk sometimes in a step wise manner keeping a close eye on the growth of the infant.


Click here to view our research papers relating to preterm nutrition. Click here to view more information on Cow & Gate preterm formulae.Click here for a podcast relating to this article.