Supplementary Material for: In Preterm Infants, Length Growth below Expected Growth during Hospital Stay Predicts Poor Neurodevelopment at 2 Years

<b><i>Background:</i></b> In preterm infants, neonatal weight growth is associated with neurodevelopmental outcome but is a poor indicator of growth quality. <b><i>Objective:</i></b> The aim of this work was to measure the relationship between neonatal length growth and the 2-year neurological outcome in preterm infants. <b><i>Methods:</i></b> A total of 2,403 infants enrolled in the LIFT cohort with gestational age less than 34 weeks were studied. Neonatal observed length growth (OLG) was calculated as the change in length <i>Z</i>-score between birth and discharge. Expected length growth (ELG) was estimated based on gestational age, birth weight <i>Z</i>-score, birth length <i>Z</i>-score, gender, and observed neonatal weight growth. The difference between OLG and ELG (∆_OLG-ELG) was calculated as OLG – ELG, and infants were ranked into 3 classes depending on their ∆_OLG-ELG (≤–0.5, –0.49 to 0.49, ≥0.50 <i>Z</i>-score). We explored the relationship between ∆_OLG-ELG and 2-year neurodevelopmental outcome (<i>n</i> = 2,036), and, in a subgroup (<i>n</i> = 85), between ∆_OLG-ELG and body composition at discharge. <b><i>Results:</i></b> ELG was strongly predicted from the above-mentioned parameters (<i>R</i>² = 0.73, <i>p</i> = 0.001). OLG correlated closely with gestational age (<i>p</i> = 0.001) but ∆_OLG-ELG did not (<i>p</i> = 1.0). OLG was not associated with a 2-year nonoptimal outcome after adjustment for gestational age, but ∆_OLG-ELG ≤–0.5 was; the crude and adjusted odds ratios were 1.63 and 1.56, respectively. ∆_OLG-ELG correlated negatively with fat mass (<i>R</i>² = 0.29, <i>p</i> = 0.006) before and after adjustment for gestational age. <b><i>Conclusion:</i></b> ∆_OLG-ELG is a marker of neonatal growth that does not depend on gestational age, and may reflect quality of growth. A ∆_OLG-ELG ≤–0.5 <i>Z</i>-score is associated with a higher risk for 2-year nonoptimal neurodevelopmental outcome.