Cumulative Burden of Neonatal Morbidities and Its Impact on Medical Costs and Length of Stay in Preterm Infants: A Nationwide Study in Korea

Background: Neonatal morbidities are major determinants of clinical outcomes and healthcare utilization in preterm infants. However, population-level evidence quantifying the cumulative contribution of neonatal morbidities to neonatal intensive care unit (NICU) length of stay (LOS) and medical costs remains limited. Methods: We conducted a nationwide retrospective cohort study using the Korean Health Insurance Review and Assessment Service database. Preterm infants admitted to NICUs between 2020 and 2023 were identified. After exclusions, 30,034 infants with complete birth weight data and 31,240 with complete gestational age data were included. Major neonatal morbidities—including bronchopulmonary dysplasia (BPD), patent ductus arteriosus (PDA), sepsis, intraventricular hemorrhage (IVH), retinopathy of prematurity (ROP), necrotizing enterocolitis (NEC), and periventricular leukomalacia (PVL)—were identified using ICD-10 odes. Associations of individual morbidities and cumulative morbidity burden with NICU LOS and medical costs were evaluated using multivariable regression and generalized linear mixed models. Results: Mean NICU LOS was 26.5 days, and mean total medical cost was 41.9 million KRW. All major morbidities were associated with prolonged LOS and increased costs. BPD showed the strongest association with LOS, whereas NEC and sepsis were associated with the highest costs. NICU LOS and medical costs increased in a stepwise manner with increasing numbers of morbidities; each additional morbidity was associated with an 8.0-day increase in LOS and a 32.5 million KRW increase in medical costs (both p < 0.001). Conclusions: Greater cumulative morbidity burden was associated with prolonged hospitalization and increased healthcare costs in preterm infants.