Urine sodium concentration and 28-day weight velocity in preterm infants: A retrospective cohort study.

Background: Urine sodium concentration has been suggested as a marker to guide enteral sodium supplementation in preterm infants; however, no previous data have demonstrated relationships between urine sodium concentration and postnatal growth.

Methods: We performed a single-center retrospective cohort study on 224 preterm infants admitted to the neonatal intensive care unit at the Children's Hospital of Georgia between January 2010 and July 2022. Spot urine sodium was measured in preterm infants (<34 weeks postmenstrual age [PMA]) between days of life (DOLs) 7 and 28. Our exposure of interest was spot urine sodium concentration (milliequivalents per liter) obtained between postnatal days 7 and 28, and our primary outcome was weight velocity (grams per kilograms per day) determined at DOL 28. Statistical relationships were assessed by multivariate analysis with subgroup comparisons by Student t test and analysis of variance.

Results: In 224 preterm infants (199 ± 17 days, 56% male, 71% Black), urine sodium concentration did not associate with weight velocity at DOL 28 and 36 weeks PMA. Urine sodium concentration was weakly associated with gestational age at birth, and Black preterm infants had higher urine sodium values when compared with "other," but not White preterm infants.

Conclusion: Spot urine sodium during the first month of life does not associate with weight velocity at DOL 28 or 36 weeks PMA.