Staying Alive

Infants born preterm and low in weight have special nutritional needs to survive and grow normally

By Lucio Victor Jr.

Technological advances in neonatology and nutrition have done much in the last two decades to steadily improve the survival odds of infants born preterm and low in weight. Millions of babies born on the brink of death have not only been given a new lease on life with timely and proper nutritional intervention; they have grown and lived normal, healthy lives.

    As it is, birth cuts off in one sudden snap of a pair of scissors the only sustenance a fetus has had while in the womb. According to Dr. Ekhard Ziegler, director of the Fomon Infant Nutrition Unit at the University of Iowa, this sudden cessation of nutrition from the mother to the fetus causes the fetus to go into a state of acute starvation. With normal births, acute starvation is immediately remedied once the infant is breastfed. But such is not the case for babies born preterm who, aside from having been deprived of much needed in utero nutrition in the final trimester, are in no position to be fed normally.

Survival of the Fittest

    To achieve homeostasis in the preterm and low-birth-weight (LBW) infants, Dr. Ziegler says parenteral support of electrolytes, water, and macromolecules is provided at the soonest possible time. In the United States, most infants weighing under 1,250 grams receive parenteral nutrition at least 36 to 48 hours after birth.

    Early parenteral nutrition consisted of water, glucose, and electrolytes. In the late 1980s, amino acids, minerals, vitamins, and lipids were gradually added. Studies since 1989 have shown that the addition of amino acids improved nitrogen balance improved and whole body protein synthesis.

    Amino acids are started at 0.5 to 10g/kg/day, and increased gradually. Essential fatty acids in lipid emulsions given at amounts not more than 1g/kg/day for the first seven days are deemed safe. Essential vitamins in nutrient solutions are likewise given soon after.

    Although parenteral nutrition in the acute setting is very important, small volumes of trophic feedings are often taken for granted. Trophic feeding or gut priming is important to prevent gastrointestinal atrophy without putting undue stress on the immature gut. Trophic feeding also improves feeding tolerance and decreases serum bilirubin concentration. Although nutrition is basically delivered parenterally, nourishment and stimulation of the gut is also important so that once discharged, the infant can feed independently. Dr. Ziegler says breast milk remains best for trophic feedings.

Keeping Up

    In an exclusive interview, Dr. Robert Hall, chief of the Division of Human Development at the Children's Mercy Hospital and Clinics in Kansas City, stressed the need for nutritional follow-up. This is because these babies have to grow at the same rate as infants born full term. In accordance with recommendations from the American Academy of Pediatrics, the goal is to reach intrauterine accretion rates.

    Dr. Hall explained that since fetal growth during the last trimester of pregnancy is very rapid and the placenta extracts more nutrients from the mother to sustain the fetus's growth, this is also the time when the fetus is very vulnerable to severe undernutrition. Preterm birth cuts short the growth and development that would have been achieved in utero. And if the mother is nutritionally deficient to begin with, the placenta is unable to sustain the baby's rapid growth in utero.

    Nutritional follow-up ensures that the preterm or LBW infant gets the nutrients it should have gotten in utero. Breast milk easily provides most of the nutrients needed. However, Dr. Hall notes: "Breast milk doesn't have enough protein, calcium, phosphorus, and other minerals to make babies grow the way they would have inside the womb. This is the reason for use of breast milk fortifiers. [This way] we are able to provide more protein, fats, carbohydrates, vitamin D, calcium and phosphorus and other minerals."

    And because some premature and LBW infants are born with multiple congenital anomalies, Dr. Hall says there are specific formulas that address specific types of congenital malformations.

    Children with CHF for example will benefit greatly from a low solute formula that contains less salt and higher amounts of protein. Energy intake is also increased from an average of 20 calories to as high as 24 to 30 calories per ounce. Infants with gastrointestinal tract malformations have absorption problems so they are given formulas that have pre-digested or hydrolyzed proteins and medium chain triglycerides, which are easier to absorb. Low-lactose formulas are also available for babies born with a short gut or lactose intolerance.

    Says Dr. Hall: "The most important thing pediatricians should do is to make sure premature and LBW babies gain 10 to 15 grams of weight per day, increase in length by one centimeter and head circumference by 0.7 centimeters per week." Before leaving the hospital these babies must have been weaned from the incubator, weigh at least 1,800 to 2,000 grams, and have no sleep apnea.

Milky Concerns

    If targets are not met, formulas with higher contents of protein, fats, calcium, phosphorus, and other vitamins but lower carbohydrates are used. Or breast milk is fortified. Growth should be monitored by regularly measuring the length, head circumference, and weight. If the babies remain below par for their age group, exclusive breastfeeding supplemented by preterm formulas or fortified breast milk will have to be continued.

    Breast milk is best because apart from providing complete nutrition, it contains maternal antibodies that confer protection against various diseases like sepsis, infectious diarrhea, upper respiratory, urinary tract infections, and necrotizing enterocolitis. Breast milk also supports the growth of bifidobacteria, which crowd out potentially pathogenic gram negative enterobacteria.

    Dr. Hall says that breastfed infants have better neurodevelopmental outcome, primarily because of the essential fatty acids present in breast milk. Mother's milk contains long chain polyunsaturated fatty acids (LCPUFAs) like arachidonic acid (AA) and decosahexaenoic acid (DHA) that are used for the structure and function of the brain and the blood vessels supplying oxygen and nutrients to it.

    But here's the downside. Dr. Hall says it does not necessarily support catch-up growth in premature and LBW infants. To get around this problem, Dr. Hall encourages breastfeeding supplemented with one or two feedings of premature formula or fortified breast milk.

Recommendations

    Dr. Marie Christine Secretin, scientific advisor of Nestlé Switzerland, lists the following concerns in deciding on what formula to give premature and LBW babies: energy density, protein requirements and quality, amino acid profile, fat absorption, LCPUFAs, calcium and phosphorus ratio, and bone mineralization.

    According to her, high energy density formulas have higher osmolarity, which increases the risk of developing necrotizing enterocolitis and adds burden to the premature infant's kidneys thereby causing dehydration. On the other hand, low energy formulas raise the risk of developing patent ductus arteriusis. She recommends a 70 to 85 kcal/100 ml energy density range.

    As for protein requirements of LBW babies, Dr. Secretin says the consensus drawn up by professors Tsang and Lucas adopts a range of 3.6 to 3.8 g/kg/day for infants less than one kilogram and 3.0 to 3.6 g/kg/day for those weighing between 1.0 to 1.75 kilograms.

    Moreover, Dr. Secretin stresses that the amino acid profile of any milk supplement should resemble that of human milk as close as possible. The standard amino acid profile of whey adapted formulas with a casein-whey ratio of 40:60 is only deficient in tryptophan but sufficient in all other essential amino acids.

    Fat absorption in preterm infants is not as efficient as in term infants. Their physiologic mechanisms are not yet fully developed due to their low lipase and bile salt levels. Medium chain triglycerides can be absorbed without the benefit of bile salts, sparing available bile salts for the absorption of long chain triglycerides (LCT). MCTs also have favorable effects on calcium, phosphorus, and magnesium absorption.

    Cerebral LCPUFAs, says Dr. Secretin, increase three to five times in utero during the third trimester. Since preterm babies are not able to complete the third trimester, they lack significant levels of DHA and AA. They are also unable to convert the LCPUFA precursors--linoleic and alpha linolenic acid--into AA and DHA.

    Dr. Secretin says adding DHA and AA to the diet of preterm infants helps improve retinal function and visual acuity. But she points out there has to be a balance between AA and DHA levels in formulas for LBW and preterm infants, and a prudent amount of vitamin E has to be added so that AA and DHA will not be oxidized and rendered useless.

    Calcium and phosphorus requirements are higher in premature infants than in term infants, that cannot be provided in full by breast milk. Dr. Secretin says the calcium/phosphorus ratio has to be adjusted to meet the high demands of preterms. Use of calcium glycerophosphate is recommended since using only calcium can cause sedimentation and blocking of feeding tubes. Calcium glycerophosphate is more soluble, is easily absorbed, and provides good levels of calcium and phosphorus.