Clinical characteristics of necrotizing enterocolitis occurring within the first week of life in low-birth-weight preterm infants: a multicenter retrospective study.

OBJECTIVES: This study aimed to compare the perinatal background, clinical characteristics, and outcomes of low-birth-weight preterm infants with Necrotizing enterocolitis (NEC) occurring within the first week of life and those with NEC occurring after the first week of life. METHODS: This multicenter retrospective study included preterm infants with a birth weight <2,500 g who were diagnosed with NEC within 28 days of life across five neonatal intensive care units from January 2021 to June 2024. Infants were classified according to age at NEC onset into an early-onset NEC group (EO-NEC, ≤7 days) and a later-onset NEC group (LO-NEC, >7 days). Perinatal characteristics, disease severity, hematological parameters, imaging findings, treatment, and short-term outcomes were compared between groups. RESULTS: Among 405 eligible infants, 151 (37.3%) developed EO-NEC. Compared with LO-NEC infants, EO-NEC infants had higher gestational age and birth weight but were more likely to be small for gestational age (SGA) and exposed to maternal hypertensive disorders. EO-NEC was also associated with a higher proportion of non-full enteral feeding before onset, Bell stage III disease, intestinal perforation, thrombocytopenia, and higher hemoglobin and hematocrit levels. However, surgical intervention and mortality did not differ significantly between groups. CONCLUSION: These findings suggest that NEC occurring within the first week of life has several characteristic clinical features and may help identify infants who require closer abdominal and hematological monitoring.