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.

**背景：** 对于早产儿而言，新生儿体重增长与神经发育结局相关，但并非生长质量的良好评估指标。
**目的：** 本研究旨在探讨早产儿新生儿身长增长与2年神经发育结局之间的关联。
**方法：** 本研究共纳入2403名参与LIFT队列、胎龄小于34周的早产儿进行分析。新生儿实测身长增长（observed length growth, OLG）通过出生至出院期间身长Z评分（Z-score）的变化量计算得到；预期身长增长（expected length growth, ELG）则基于胎龄、出生体重Z评分、出生身长Z评分、性别以及新生儿实测体重增长进行估算。实测身长增长与预期身长增长的差值（∆_OLG-ELG）通过OLG减去ELG计算得到，并根据该差值将早产儿分为3组：≤-0.5 Z评分、-0.49至0.49 Z评分、≥0.50 Z评分。本研究分析了∆_OLG-ELG与2年神经发育结局的关联（有效样本量n=2036），同时在亚组分析（n=85）中探讨了∆_OLG-ELG与出院时身体成分的关系。
**结果：** 基于上述参数可较好预测ELG（决定系数R²=0.73，p=0.001）。OLG与胎龄密切相关（p=0.001），但∆_OLG-ELG与胎龄无关联（p=1.0）。在校正胎龄后，OLG与2年不良神经发育结局无显著关联，但∆_OLG-ELG≤-0.5的早产儿则存在该关联；未校正与校正后的比值比分别为1.63和1.56。在校正胎龄前后，∆_OLG-ELG均与脂肪量呈负相关（R²=0.29，p=0.006）。
**结论：** ∆_OLG-ELG是不依赖胎龄的新生儿生长指标，可反映生长质量；∆_OLG-ELG≤-0.5 Z评分与2年不良神经发育结局的更高风险相关。