Epidemiology of Necrotizing Enterocolitis in Multi-Birth Preterm Infants: A 22-Year Retrospective Study in Switzerland (2000-2021).

Background Necrotizing enterocolitis (NEC) is a life-threatening gastrointestinal condition predominantly affecting preterm infants. Although multiple births are increasingly common, their specific contribution to NEC risk remains unclear. Objective To assess the incidence and mortality of NEC in preterm multiple-birth infants in Switzerland over two decades (2000-2021), and to determine whether multiplicity contributes to NEC risk. Methods We conducted a retrospective cohort study of 15,635 infants born before 32 weeks' gestation, using prospectively collected data from the Swiss Neonatal Network. Results Of the cohort, 32.8% (n = 5133) were multiple births. The overall NEC incidence was 2.84%, with no statistically significant difference between singletons (2.9%) and multiples (2.7%). NEC-related mortality was high (35.8%) and similar across groups (35.3% in multiple births vs. 36% in singletons). However, within twin pairs, if one twin developed NEC, the second twin's odds increased sixfold (OR 6.1, 95% CI 2.4-16.2). NEC incidence remained stable over the study period. Conclusion Over a 22-year period, incidence and mortality of NEC in preterm multiple-birth infants in Switzerland remained stable and did not differ significantly from those in singletons. Multiple gestation was not a risk factor for NEC. However, within twin pairs, the diagnosis of NEC in one twin was associated with a sixfold increased odds (OR 6.1, 95% CI: 2.4-16.2) of NEC in the co-twin, raising the estimated risk from 2.7% to 15%. This clustering suggests shared environmental or biological triggers. These findings underscore the importance of vigilant surveillance in the co-twin of an affected infant.