Fenton vs INTERGROWTH-21st charts in preterm infants < 32 weeks: impact of chart selection on growth classification

Monitoring postnatal growth in preterm infants is essential to detect extrauterine growth restriction (EUGR) and guide nutritional management. The Fenton and INTERGROWTH-21st (IG-21) charts are commonly used for this purpose, but their agreement and clinical relevance remain uncertain. This study aimed to compare postnatal growth assessment using Fenton and IG-21 charts in infants born before 32 weeks' gestation and to evaluate differences in static and dynamic growth classification. We conducted a prospective single-center cohort study of preterm infants < 32 weeks admitted between January 2023 and June 2024. Weight, length, and head circumference were measured at birth, 15 days, 1 month, and discharge. Z-scores were calculated using  both charts, and growth classifications were compared using WHO standards as reference. Statistical analyses included Wilcoxon, McNemar, and linear mixed-effects models. A total of 158 infants were included. At birth, IG-21 classified more infants as small for gestational age (20% vs 13%, p < 0.01) and with low head circumference (12% vs 8%, p = 0.03). At discharge, IG-21 identified more infants with low weight (50% vs 44%, p = 0.03) and microcephaly (14% vs 3%, p < 0.01). Growth faltering was more frequent with IG-21 (31% vs 25%, p < 0.01), while Fenton detected more infants with ≥ 1 or ≥ 2 z-score declines (p < 0.05). Both charts underestimated EUGR prevalence compared with WHO (63%). Mixed-effects models confirmed significant declines in weight, length, and head circumference over time (p < 0.001), particularly  for length and head circumference.

Growth chart selection substantially affects how preterm infants are classified. IG-21 applies stricter static thresholds, whereas Fenton identifies more dynamic declines over time. Using both static and longitudinal assessments may provide a more accurate evaluation of postnatal growth and support individualized nutritional decisions in very preterm infants.

• Postnatal growth monitoring in very preterm infants is important to detect extrauterine growth restriction and guide nutritional strategies. • Different growth charts, including Fenton and INTERGROWTH-21st, are used in clinical practice, but they differ in design, reference populations, and intended applications. • The clinical interpretation of postnatal growth and growth faltering in very preterm infants remains challenging, particularly when different charts yield discordant classifications.

• In infants born before 32 weeks' gestation, growth classification differs substantially depending on the growth chart used. • INTERGROWTH-21st applies stricter static cut-offs, whereas Fenton identifies a higher proportion of longitudinal declines in zscores during hospitalization. • Combining static and longitudinal growth assessments may improve the evaluation of postnatal growth and better inform individualized nutritional management in very preterm infants.