(Source: Ronesca Website)
Preterm babies are born before 37 weeks of gestation and will weigh much less than babies who have gone to term. This is because infants in the womb will gain significant weight between the weeks 36-40. Preterm babies need to catch up on this loss.
Preterm Infants are classified as:
Low birth weight (LBW): less than 2.5kg (5,5lbs)
Very low birth weight (VLBW): between 1kg (2.2lbs) and 1.5kg (3.3lbs)
Extremely low birth weight (ELBW): less than 1kg (2.2lbs)
The aim in feeding preterm babies is to achieve the same growth rate as a normal fetus of the same gestational age1. Much of the stores and body reserves of the infant in the uterus are received and laid down via the umbilical cord and placenta during the third trimester. A preterm baby, therefore tends to have low stores and needs the correct nutrients to achieve catch-up growth.
A statement for ESPGHAN (The European Society of Paediatric Gastroenterology, Hepatology and Nutrition) highlights the fact that ‘those preterm infants who fail to achieve their growth potential during the first weeks of post-natal life have a less favourable outcome with respect to growth and neurodevelopment’2.
Preterm infants often also have immature physiology and digestive enzymes that are not fully functional and they can often not initially tolerate feeds by mouth.
Depending on their maturity and overall health, they will receive nutrients in a combination of ways. This can be through total parenteral nutrition, a combination of parenteral and minimal enteral feeding or through full enteral feeding.
Better outcomes in the management of preterm infants due to advances in nutrition have resulted in new guidelines for LBW, VLBW and ELBW infants.
The Tsang Guidelines (2005)3 are the result of several experts combining their efforts to make recommendations for nutrients and energy intakes. They include information on specific nutrients – proteins, carbohydrates, vitamins & minerals, water & electrolytes and lipids. Also examined are the roles of enteral and parenteral feeding along with that of breast milk.
The LSRO (Life Sciences Research Office) Guidelines4 were released in 2002 in the USA and address the nutrient content of infant formulas for preterm and low birth weight infants. LSRO is a mixture of permanent staff and outside consultants who provide objective scientific advice. They brought together a panel of world experts to make recommendations for the best clinical care of premature infants from birth to leaving hospital.
Nutrition for Preterm Infants
The aim of nutritional management of a preterm infant is to achieve full enteral feeding as soon as possible. If enteral feeding (by tube) is not initially possible, intravenous nutrition is given where nutrients are passed into the bloodstream – often using the umbilical vein.
Total Parenteral Nutrition (TPN)
This is also known as hyperalimentation. The need for it can be due to feed intolerance, gastric disease or just while enteral nutrition is being established. Very low birth weight infants can take time to tolerate gastric tube feeds1 as they often have delayed gastric emptying and intestinal peristalsis.
Survival rates of infants who would not otherwise have had enough nutritional support, have significantly improved with the provision of parenteral nutrition2.
TPN rapidly provides the preterm infant with vital nutrition3. It also helps to achieve a positive nitrogen balance by reducing tissue catabolism4.
It is important to be aware of possible problems, however. Bloodstream infections are the most common complication and TPN has been associated with hyperbilirubinemia and hyperglycemia2. Infants can also suffer too high or too low a level of vitamins due to bypassing the usual absorption regulators and sole use of parenteral nutrition with an absence of nutrients in the gut can lead to gut atrophy5.
For preterm infants of more than 34 weeks of gestation, it is possible that breast or bottle feeding can be adopted as they should be able to coordinate sucking, swallowing and breathing.
But for those younger infants who may have compromised respiration or be neurologically less well developed, this may not be advisable1 and nutrients may need to be passed into the stomach through a fine tube either through the mouth (oro-gastric) or the nose (naso-gastric). Breast milk is the food of choice as it is best tolerated and includes other benefits as well as nutrition.
For the first few days, very small preterm infants can be given ‘minimal enteric feedings’, also known as ‘trophic’ or ‘non-nutritive’ feeds. These are given in very small volumes due to the inability to cope with large feeding volumes6.
Minimal enteral feeding should be begun as soon as is possible as it promotes improved weight gain7,8 and a quicker ability to cope with full enteric feeds9. Also, whole gut transit is reduced10, intestinal motility10 and lactose activity11 are increased and gastrointestinal hormone release is stimulated11.
If possible, parents should be allowed to help with tube feeding to promote ‘skin-to-skin’ contact and help build a bond with baby.
Moving on from tube-feeding
Preterm infants are just like any other babies – some learn more quickly than others and parents will often need reassurance. It can take weeks before a sucking reflex is established well enough for baby to feed properly as this also depends on their general condition and how prematurely they were born.
If a baby being tube fed starts opening and closing their mouth during the feed, they are probably ready to practice sucking. Giving them a dummy (pacifier) can often help develop the reflex. It has been shown that this can help the preterm baby make the move from tube-feeding to normal feeding1.
Sometimes called ‘non-nutritive suckling’, this has also been shown to help with gastric motor functions2 and craniofacial/dental development3.
As soon as possible after birth, mothers should be encouraged to express breast milk as often as they can. This can then be frozen and stored for when the baby is ready to take it.
But for those mothers in hospital who are not able to provide breast milk, a specially designed low birth weight infant formula is available. This contains the particular nutrients in proportions that the preterm baby needs and will usually be given by naso-gastric or oro-gastric tube until baby can manage the sucking/swallowing/breathing process when they can begin to be bottle-fed.
Even by the time they leave hospital, low birth weight/preterm infants weigh less4,5 and have lower nutrient stores than term babies6. Specially developed ‘Premature formulas’ have been created to provide the extra protein, energy, vitamins and minerals needed by preterm infants.
How long an infant will need to stay on a Premature formula will depend on their individual weight and progress. The smaller the premature baby is at birth, the more benefit is likely to be derived from an enriched premature formula. There are no established guidelines for when a premature formula should be used or for when the transition to a ‘term’ formula should be made but clinical studies have demonstrated benefits of premature formulas for up to12 months.
Their use is recommended by ESPGHAN (The European Society of Paediatric Gastroenterology, Hepatology and Nutrition) until a post-conceptual age of 40-52 weeks7. The observation of the Committee on Nutrition, American Academy of Pediatrics 2009 is that premature formulas are often continued until 9-12 months corrected age or till the baby’s weight for age is maintained above the 25th percentile8.