Genetic and environmental components of neonatal weight gain in preterm infants.

BACKGROUND AND OBJECTIVES: Postnatal nutrition and subsequent weight gain or failure in the neonatal period are likely regulated by both the environment and the genetic background. With the goal of estimating the variability of postnatal weight gain due to genes and environment, comparison between monozygotic (ie, genetically identical) and dizygotic (genetically similar as 2 siblings) twins can be performed. METHODS: This study selected a very homogenous set of monozygotic and dizygotic twins who met the following inclusion criteria: gestational age between 30 and 36 weeks, birth weight between 1250 and 2200 g, and length of stay >12 days. Opposite-gender pairs and pairs that differed >20% in terms of birth weight were excluded from this analysis. The outcome measure of this study was the daily weight gain expressed in grams per kilogram per day during the period between day of birth and day of discharge. The average difference between members of a pair was computed in the 2 groups of twins, and heritability was estimated. RESULTS: The within-pair differences of the outcome measure were lower for monozygotic twins than for dizygotic twins, suggesting a strong genetic component. The total variance of the phenotype under study is explained by 2 sources of variation, additive genetic (87% [95% confidence interval: 67% to 94%]) and unique environment (13% [95% confidence interval: 6% to 33%]) components. CONCLUSIONS: This high heritability estimate could suggest using this set of criteria to identify genes that regulate postnatal weight gain or failure.

Feeding intolerance in preterm infants. How to understand the warning signs.

It is essential to start enteral nutrition early to preterm infants by giving small amounts of milk (preferably human milk) to ensure that metabolic homeostasis is kept stable and to limit postnatal growth retardation. Increasing feeding volumes to reach "full enteral feeding" is limited by individual feeding tolerance. Feeding intolerance is extremely common in premature infants. The most frequent signs of a suspect feeding intolerance are the presence of gastric residuals, abdominal distension and the onset of crises of apnea/bradycardia. Gastric residuals are probably a benign consequence of delayed gut maturation and motility in VLBW infants and there are no established normal standards. When gastric aspirates occur isolated they should not immediately induce the neonatologist to withhold feeding. Gastric residual becomes more important when accompanied by other warning signs, such as bilious vomiting, abdominal distension, abdominal wall erythema or ecchymosis, gross or occult blood in the stool, apnoea, bradycardia and temperature instability. Nutrition protocols in preterm infants must take caution when starting and increasing enteral feeding, and pay proper, but not excessive, attention to early signs of food intolerance.