Neonatal intraventricular hemorrhage prevention bundles for preterm infants commonly defer daily weighing for the first 72 h, with reweighing occurring on day 4.

Clinicians rely on maintaining stable sodium values as a proxy of fluid status to inform fluid management decisions over the first 96 h after birth.

Yet, there exists a paucity of research evaluating whether serum sodium or osmolality are appropriate proxies for weight loss and whether increasing variability in sodium or osmolality during this early transitional period is associated with adverse in-hospital outcomes.

We evaluated whether serum sodium or osmolality change in the first 96 h after birth was associated with percent weight change from birth weight, and to assess potential associations between serum sodium and osmolality variability with in-hospital outcomes.