Postnatal growth failure is a significant morbidity in very low birth weight (VLBW, <1500 grams at birth) infants. Efforts to promote growth and optimize nutritional support have included earlier initiation of parenteral nutrition and increased caloric and protein administration. While these advances in nutritional practices have resulted in improved growth, up to 50% of VLBW infants continue to experience postnatal growth failure (defined as discharge weight <10th percentile by Fenton growth charts) and over 25% experience severe postnatal growth failure (<3rd percentile). Current nutritional recommendations for sodium provision to preterm infants is 3-5 mEq/kg/d and fails to take into account the degree of renal immaturity present in extremely preterm infants. The investigators hypothesize that the sodium supplementation algorithm will improve in-hospital somatic growth (weight, length, and head circumference) between 2 weeks of postnatal age and 36 weeks postmenstrual age over current sodium replacement practices. The algorithm will be evaluated in a prospective, pragmatic, randomized trial. Infants in the sodium supplementation algorithm group will have a spot urine sodium concentration determined every two weeks beginning on the 14th postnatal day and continuing until 36 weeks postmenstrual age with sodium supplementation provided according to the algorithm.
Postnatal growth failure occurs in up to 50% of very low birth weight (VLBW, <1500 grams at birth) infants as assessed by discharge weight. This study will evaluate if a sodium supplementation algorithm guided by spot urine sodium measurements can improve postnatal growth.