Risk Factors and Effects of Severe Late-Onset Hyponatremia on Long-Term Growth of Prematurely Born Infants

PURPOSE: Sodium is an essential nutritional electrolyte that affects growth. A low serum sodium concentration in healthy premature infants beyond 2 weeks of life is called late-onset hyponatremia (LOH). Here, we investigated the association between LOH severity and growth outcomes in premature infants. METHODS: Medical records of premature infants born at ≤32 weeks of gestation were reviewed. LOH was defined as a serum sodium level <135 mEq/L regardless of sodium replacement after 14 days of life. Cases were divided into two groups, <130 mEq/L (severe) and ≥130 mEq/L (mild). Characteristics and growth parameters were compared between the two groups. RESULTS: A total of 102 premature infants with LOH were included. Gestational age ([GA] 27.7 vs. 29.5 weeks, p<0.001) and birth weight (1.04 vs. 1.34 kg, p<0.001) were significantly lower in the severe group. GA was a risk factor of severe LOH (odds ratio [OR], 1.328, p=0.022), and severe LOH affected the development of bronchopulmonary dysplasia (OR, 2.950, p=0.039) and led to a poor developmental outcome (OR, 9.339, p=0.049). Growth parameters at birth were lower in the severe group, and a lower GA and sepsis negatively affected changes in growth for 3 years after adjustment for time. However, severe LOH was not related to growth changes in premature infants. CONCLUSION: Severe LOH influenced the development of bronchopulmonary dysplasia and developmental outcomes. However, LOH severity did not affect the growth of premature infants beyond the neonatal period.