Supplementary Material for: How Should We Define Postnatal Growth Restriction in Preterm Infants?

Background: Postnatal growth restriction is very common among preterm infants. Growth restriction might be associated with neurodevelopment impairment. The definition of postnatal growth restriction varies among studies. It has often been based on statistical parameters, but we lack biological data to support this definition. Objectives: The aim here was to study the association between neurodevelopment and postnatal growth restriction defined applying 2 different strategies. Methods: Bayley Scales of Infant Development-II was performed at 2 years corrected age in 168 preterm infants. Postnatal growth restriction was defined as a weight z-score at 36 weeks <–1.5 or treated as a continuous variable (fall in weight z-scores from birth to 36 weeks postmenstrual age). Results: Weight z-scores fell in almost all patients (98.8%), and 44.1% had z-scores <–1.5 at 36 weeks. After adjusting for gestational age and small for gestational age at birth, every 1-point fall in weight z-score was associated with a 5.6 point (95% CI 1.7 to 9.4) decrease in the Mental Developmental Index. A weight z-score <–1.5 at 36 weeks was not associated with a worse mental or psychomotor result. Conclusion: A fall in the weight z-score from birth to 36 weeks is a more rational definition of postnatal growth restriction, and it could predict neurodevelopment.