Reclassification of SGA and EUGR in very preterm infants after the introduction of Fenton-2025: a retrospective cohort comparison with INTERGROWTH-21st and Fenton-2013

BACKGROUND: In very preterm infants, the classification of small for gestational age (SGA) and extrauterine growth restriction (EUGR) depends on the growth chart used. In this context, the classification implications of the newly introduced Fenton-2025 curves have not yet been evaluated in this population. We compared SGA and EUGR classification across Fenton-2025, INTERGROWTH-21st, and Fenton-2013, and examined chart-specific associations between EUGR and major neonatal morbidities. METHODS: This retrospective single-centre cohort study included 272 infants born at 24-32 weeks' gestation. SGA was defined as birth weight below the 10th percentile. EUGR was defined as discharge weight-for-age Z score below - 2. Associations between chart-defined EUGR and neonatal morbidities were examined using multivariable logistic regression adjusted for gestational age, birth weight, and sex. RESULTS: SGA rates differed in rank order across the three charts, being lowest with Fenton-2013 (9.9%), intermediate with INTERGROWTH-21st (15.8%), and highest with Fenton-2025 (24.3%). For EUGR, the ordering was different: rates were lowest with INTERGROWTH-21st (26.1%), intermediate with Fenton-2013 (33.5%), and highest with Fenton-2025 (40.8%). Despite this difference in rank order, the three charts showed a nested classification pattern. Compared with INTERGROWTH-21st, Fenton-2025 classified 56% more infants (n = 40) as EUGR. Nevertheless, in adjusted analyses, infants classified as EUGR according to the Fenton 2013 and INTERGROWTH-21st charts were associated with higher adjusted odds (aOR 6.37, 95% CI 2.07-19.57, and aOR 5.03, 95% CI 1.82-13.90, respectively) of necrotising enterocolitis (≥ stage II) compared to non-EUGR infants, and this higher adjusted odds persisted after reclassification using the Fenton 2025 chart (aOR 4.96, 95% CI 1.68-14.64). CONCLUSIONS: Fenton-2025 applies a more inclusionary approach in classifying very preterm infants as SGA and EUGR compared with INTERGROWTH-21st and Fenton-2013. The clinical implications of this broader classification require further outcome-linked validation.