BMJ  2004;329:1227-1230 (20 November), doi:10.1136/bmj.329.7476.1227

Clinical review

ABC of preterm birth

Feeding the preterm infant

Introduction

Providing appropriate nutrition for growth and development is a cornerstone of the care of preterm infants. Early postnatal nutrition during this critical period of brain growth may have a substantial impact on clinically important outcomes, including long term neurodevelopment.

Preterm infants, especially those who have been growth restricted in utero, have fewer nutrient reserves at birth than term infants. Additionally, preterm infants are subject to physiological and metabolic stresses that can affect their nutritional needs, such as respiratory distress or infection. An international consensus group has recommended nutritional requirements for preterm infants. These recommendations are based on data from intrauterine growth and nutrient balance studies and assume that the optimal rate of postnatal growth for preterm infants should be similar to that of normal fetuses of the same postconception age. In practice, however, these target levels of nutrient input are not always achieved and this may result in important nutritional deficits.

View this table: [in this window] [in a new window]   Nutritional requirements for preterm infants*

 

Enteral feeding

Well infants of gestational age > 34 weeks are usually able to coordinate sucking, swallowing, and breathing, and so establish breast or bottle feeding. In less mature infants, oral feeding may not be safe or possible because of neurological immaturity or respiratory compromise. In these infants milk can be given as a continuous infusion or as an intermittent bolus through a fine feeding catheter passed via the nose or the mouth to the stomach.

Necrotising enterocolitis
A major concern with the introduction of enteral feeds (especially to very preterm, growth restricted, or sick infants) is that the additional physiological strain on the immature gastrointestinal tract may predispose to the development of necrotising enterocolitis. The risk of necrotising enterocolitis is inversely related to gestational age and birth weight. The incidence is 5-10% in very low birth weight infants. The mortality rate is reported consistently as greater than 20%. Long term morbidity may include substantial neurodevelopmental problems, the consequence of undernutrition and associated infection during a vulnerable period of growth and development.

View this table: [in this window] [in a new window]   Presenting clinical features of necrotising enterocolitis

 

Most preterm infants who develop necrotising enterocolitis have received enteral feeds. At present, however, limited evidence exists that the way that we feed infants who are at risk affects the incidence of necrotising enterocolitis. Large randomised controlled trials are needed to determine whether strategies, such as delaying the introduction of milk feeds or delivering only minimal enteral nutrition, influence clinically important outcomes for preterm infants. Apart from assessing the impact of feeding strategies on short term outcomes, such as growth, and the risk of necrotising enterocolitis, trials should also determine how various enteral feeding strategies affect mortality and long term neurodevelopment.

View this table: [in this window] [in a new window]   Minimal enteral nutrition—main points

 

Which milk?

Human breast milk is the recommended form of enteral nutrition for preterm infants. The milk could be from the infant's mother or expressed milk from donor mothers, who are usually mothers who have delivered term infants. The nutrient content of expressed breast milk varies depending on the stage of lactation at which it is collected. Milk expressed from a donor's lactating breast has a higher calorie and protein content than that collected from the opposite breast (drip breast milk).

View this table: [in this window] [in a new window]   Typical nutritional contents of human expressed breast milk (per 100 ml)*

 

Human breast milk, particularly donated drip breast milk, may not consistently provide all of the nutrient requirements of preterm infants. Multinutrient fortifiers are available to add to human milk to achieve these targets. Fortification of human milk with calcium and phosphate may improve bone mineral content. Protein and energy supplementation of human milk increases the rate of weight gain and head growth, at least in the short term. Long term follow up studies are needed to determine if nutrient fortification of human milk improves neurodevelopmental outcomes for preterm infants.

Human breast milk has non-nutrient advantages for preterm infants, primarily through the delivery of immunoprotective and growth factors to the immature gut mucosa. Some evidence exists that preterm infants who receive human breast milk rather than formula milk have a lower incidence of feed intolerance and gastrointestinal upset, and a lower incidence of necrotising enterocolitis.

Supporting mothers to express breast milk
Mothers may be very anxious after preterm delivery, especially if their infant needs intensive care. Although feeding might not be seen as an immediate concern, mothers should be aware that providing breast milk is one of the most important parts of their infant's care. In developing countries, supporting mothers to provide expressed breast milk may be the most important intervention available for preterm infants. Feeding with expressed human milk reduces the risk of serious infection, which is a major cause of neonatal morbidity and mortality in preterm infants in developing countries.

View larger version (23K): [in this window] [in a new window]   Relative risk of confirmed necrotising enterocolitis with human milk versus formula. Adapted from McGuire W, Anthony MY. Arch Dis Child 2003;88: 11-14

 

Various initiatives may help mothers who are expressing breast milk:

• Early discussion of breast feeding
  
• Written information
  
• Frequent expression
  
• Simultaneous expression of both breasts
  
• Breast massage
  
• Use of electric pump
  
• Skin to skin contact
  
• Sucking from as early as 32 weeks after conception
  
• Cup feeding
  
• Continued support and education.
  

The initiation of skin to skin contact between mother and infant (although not always possible for lengthy periods of time with extremely preterm infants) can help with bonding, milk production, and the subsequent establishment of breast feeding. Milk can be delivered via a gastric tube or by cup feeding while the infant is learning to suck at the breast. Bottle feeding should be avoided as it may interfere with the establishment of breast feeding.

Donor milk banking
Use of donor milk for preterm infants has declined over the past 20 years. This fall is caused by concerns about the nutritional adequacy of donor breast milk, the resources needed to pasteurise and store donated milk, and the cost and feasibility of screening donors for transmissible infections, such as the human immunodeficiency virus. In several countries, efforts have been made to re-establish donor milk banks that were closed in the 1980s. Economic studies show that the costs of this service may be balanced by the potential health gains associated with feeding with human milk—for example, a shorter stay in hospital.

Skin to skin care promotes bonding and milk production (left). The infant can be cup fed (right) until breast feeding is established

 

Formula milks
Despite optimal maternal support, expressed breast milk may not always be available. As an alternative, preterm infants may be fed with a variety of artificial formula milks, mainly modified cow's milk. Broadly, these may be "term" formulae (based on the composition of mature breast milk), or calorie, protein, and mineral enriched "preterm" formulae (tailored to support intrauterine nutrient accretion rates). Some evidence exists that feeding very preterm infants with preterm formula milk increases the rate of weight gain and head growth, at least in the short term, and improves some neurodevelopmental outcomes. No evidence exists that feeding preterm infants with formula milk supplemented with long chain polyunsaturated fatty acids is beneficial.

View this table: [in this window] [in a new window]   Typical content of nutrient enriched preterm formula milk compared with standard term formula (per 100 ml)*

 

Parenteral nutrition

Very preterm infants, who often have relatively delayed gastric emptying and intestinal peristalsis, may be slow to tolerate the introduction of gastric tube feeds. These infants may need intravenous nutrition while enteral nutrition is being established or when enteral nutrition is not possible—for example, because of respiratory instability, feed intolerance, or serious gastrointestinal disease.

View this table: [in this window] [in a new window]   Complications of total parenteral nutrition

 

Total parenteral nutrition consists of a glucose and amino acid solution with electrolytes, minerals, and vitamins, plus fat as the principal non-protein energy source. The solutions are usually prepared in a specialist pharmacy to minimise the risk of microbial contamination. Bloodstream infection is the most common important complication of parenteral nutrition use. Delivery of the solution via a central venous catheter rather than a peripheral catheter is not associated with a higher risk of infection. Extravasation injury is a major concern when parenteral nutrition is given via a peripheral cannula. Subcutaneous infiltration of a hypertonic and irritant solution can cause local skin ulceration, secondary infection, and scarring.

Nutrition after hospital discharge

Most preterm infants, and especially very preterm infants, have an accumulated nutritional deficit when they are discharged from hospital. Iron and vitamin supplementation is necessary until infants are at least six months old, especially if they are fed on breast milk only. Protein and energy enriched formula milk may improve catch-up growth, at least in the short term. This may be of particular importance for infants with additional metabolic requirements, such as those caused by chronic lung disease. Further research is needed to determine if breast milk should be fortified after the infant is discharged.

Conclusion

The nutritional management of preterm infants may have a major impact on growth and development. Various feeding strategies are available, including the use of expressed maternal milk, donor human milk, breast milk fortifiers, adapted formula milks, and total parenteral nutrition. A lack of robust evidence exists to guide practice for many of these interventions. Large, pragmatic randomised controlled trials are needed to assess the effects of a number of these feeding strategies on clinically important outcomes for preterm infants.

Further reading • Anderson GC, Moore E, Hepworth J, Bergman N. Early skin-to-skin contact for mothers and their healthy newborn infants. Cochrane Database Syst Rev 2003;(4): CD003519 • Ainsworth SB, Clerihew L, McGuire W. Percutaneous central venous catheters versus peripheral cannulae for delivery of parenteral nutrition in neonates. Cochrane Database Syst Rev 2004;(2): CD004219 • Kennedy KA, Tyson JE, Chamnanvanakij S. Rapid versus slow rate of advancement of feedings for promoting growth and preventing necrotizing enterocolitis in parenterally fed low-birth-weight infant. Cochrane Database Syst Rev 2003;(4): CD001241 • Kennedy KA, Tyson JE, Chamnanvanikij S. Early versus delayed initiation of progressive enteral feedings for parenterally fed low birth weight or preterm infants. Cochrane Database Syst Rev 2003;(4): CD001970 • Tyson JE, Kennedy KA. Minimal enteral nutrition for promoting feeding tolerance and preventing morbidity in parenterally fed infants. Cochrane Database Syst Rev 2004;(2): CD000504 • Morley R, Lucas A. Randomized diet in the neonatal period and growth performance until 7.5-8 years of age in preterm children. Am J Clin Nutr 2000;71: 822-8[Abstract/Free Full Text] • Lucas A, Morley R, Cole TJ. Randomised trial of early diet in preterm babies and later intelligence quotient. BMJ 1998;317: 1481-7[Abstract/Free Full Text] • Cooke RJ, Embleton ND. Feeding issues in preterm infants. Arch Dis Child 2000;83: 215-8[Free Full Text] • McGuire W, Anthony MY. Formula milk versus term human milk for feeding preterm or low birth weight infants. Cochrane Database Syst Rev 2003;(4): CD002972

 

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This is the eighth in a series of 12 articles

Ginny Henderson is a neonatal nurse in the Neonatal Intensive Care Unit at Ninewells Hospital and Medical School, Dundee.

The ABC of preterm birth is edited by William McGuire, senior lecturer in neonatal medicine, Tayside Institute of Child Health, Ninewells Hospital and Medical School, University of Dundee; and Peter W Fowlie, consultant paediatrician, Perth Royal Infirmary and Ninewells Hospital and Medical School, Dundee. The series will be published as a book in spring 2005.

Competing interests: For WMcG's competing interests see first article in the series.

The photographs showing a woman expressing breast milk, skin to skin contact, and cup feeding are courtesy of the Health Promotion Agency for Northern Ireland.

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This article has been cited by other articles:

• Boyd, C. A, Quigley, M. A, Brocklehurst, P. (2007). Donor breast milk versus infant formula for preterm infants: systematic review and meta-analysis. Arch. Dis. Child. Fetal Neonatal Ed. 92: F169-F175 [Abstract] [Full text]  
• Sangild, P. T. (2006). Gut Responses to Enteral Nutrition in Preterm Infants and Animals. Exp. Biol. Med. 231: 1695-1711 [Abstract] [Full text]  
• Almeida, S. G., Dorea, J. G. (2006). Quality control of banked milk in brasilia, Brazil.. J Hum Lact 22: 335-339 [Abstract]  

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