Routine probiotics and outcomes in infants < 29 weeks: a 13-year single-centre cohort with propensity-weighted sensitivity analyses.

UNLABELLED: Probiotic supplementation in preterm infants has been associated with reduced necrotising enterocolitis (NEC) and mortality, but reported effects vary across studies due to heterogeneity in populations, probiotic products, and co-interventions, with limited representation of extremely preterm infants. We performed a single-centre retrospective cohort study of infants born at < 29 weeks' gestation admitted for intensive care between 2012 and 2024 using electronic patient records. After excluding infants who died within the first 7 days and other predefined exclusions, 581 infants were analysed: 79 (13.6%) received no probiotics and 502 (86.4%) received probiotics (two products used sequentially during the study period). Baseline characteristics (gestational age, birthweight, sex, and antenatal steroid exposure) were similar between groups. Primary outcomes were in-hospital mortality and severe NEC, defined pragmatically as NEC requiring transfer for surgical management and/or surgery. Secondary outcomes included culture-positive late-onset sepsis (LOS) and time to full enteral feeds. Associations were examined using multivariable logistic regression adjusting for gestational age, birthweight, sex, antenatal steroid exposure, and calendar year, supported by propensity-score overlap-weighted sensitivity analysis. In-hospital mortality was 4.8% in probiotic-exposed infants versus 13.9% in unexposed infants. Probiotic exposure was associated with lower adjusted odds of in-hospital mortality (aOR 0.31; 95% CI 0.10-0.93; p = 0.036). No clear association was observed with severe NEC or culture-positive LOS. CONCLUSION: In this 13-year single-centre cohort of infants < 29 weeks' gestation, routine probiotic use was associated with lower in-hospital mortality, while effects on severe NEC and LOS were not clearly demonstrated. WHAT IS KNOWN: • Probiotic supplementation in preterm infants has been associated with reduced NEC and mortality, but results vary across studies. • Prior evidence is heterogeneous, with limited representation of extremely preterm infants and variability in probiotic strains, dosing, and co-interventions. WHAT IS NEW: • In a 13-year single-centre cohort of infants < 29 weeks' gestation, probiotic use was associated with lower in-hospital mortality after adjustment. • No clear difference in severe NEC (surgery/transfer) was observed between probiotic-exposed and unexposed infants.