Two faces of necrotizing enterocolitis: early and late-onset disease in preterm infants

Background: Whether early-onset (EO-NEC) and late-onset necrotizing enterocolitis (LO-NEC) represent distinct entities remains debated. We compared clinical presentation, radiologic features, and surgical outcomes. Methods: In this retrospective study (2013–2023), neonates with Bell stage II–III NEC were stratified into EO-NEC (< 14 days) and LO-NEC (≥ 14 days). Results: Fifty-seven infants were included: 37 (64.9%) EO-NEC and 20 (35.1%) LO-NEC. EO-NEC was associated with higher birth weight (1611 ± 767 vs. 1111 ± 377 g; p = 0.0017) and gestational age (31.4 ± 4.5 vs. 29.3 ± 2.7 weeks; p = 0.033). LO-NEC occurred more frequently in very-low-birth-weight infants (55% vs. 8%; p < 0.001) and showed higher rates of portal venous gas (70% vs. 30%; p = 0.005) and indomethacin-treated PDA (25% vs. 2.7%; p = 0.031). Intestinal perforation occurred exclusively in EO-NEC (27%; p = 0.01). Surgical intervention rates, intestinal resection lengths, and mortality were comparable. Conclusions: EO-NEC and LO-NEC differ in infant maturity and perinatal exposures but not in overall severity or mortality.