Departments of Statistics and Analytical Sciences and.
Department of Psychology, College of Humanities and Social Sciences, Kennesaw State University, Kennesaw, Georgia.
Pediatrics. 2018 Sep;142(3). doi: 10.1542/peds.2017-4169.
Longitudinal growth curves, based on repeated measurements from the same group of infants, exist for preterm infant weight and length but not for BMI. Our existing BMI (weight divided by length squared) curves are based on cross-sectional birth data obtained from a different group of infants at each gestational age (GA).
We calculated BMI over time for 68 693 preterm infants between 24 and 36 weeks GA. Stratifying infants by sex, GA at birth, and quintiles based on birth BMI, we created longitudinal median curves using R and validated the resulting curves for empirical fit, proper classification, and normality of scores.
We created 2 sets of BMI growth charts. The first set displays fitted median curves for all 5 percentile groups in each GA group by sex. The second set displays fitted median curves with their corresponding third and 97th percentiles by percentile group, GA, and sex. In the validation analysis, percentage of daily observations below the median curve approximated the expected 50th percentile after the initial 3 days. Unlike the cross-sectional curves, the longitudinal curves reveal the pattern of change corresponding to nadir; postnadir, these curves remained consistently below the cross-sectional curves and varied by GA and sex as expected. The percentage of observations falling below the 50th percentile for cross-sectional curves (revealing optimal growth) was generally much higher than for longitudinal curves (revealing actual growth).
These new longitudinal curves provide clinicians data on how premature infants' body proportionality changes over time.
早产儿体重和身长的纵向生长曲线基于同一组婴儿的重复测量，但 BMI 没有纵向生长曲线。我们现有的 BMI（体重除以身长的平方）曲线基于在每个胎龄（GA）从不同组的婴儿获得的横断面出生数据。
我们计算了 24 至 36 周 GA 的 68693 名早产儿的 BMI 随时间的变化。按性别、出生 GA 和出生 BMI 五分位数对婴儿进行分层，我们使用 R 计算了 BMI 的纵向中位数曲线，并验证了这些曲线在经验拟合、正确分类和分数的正态性方面的有效性。
我们创建了 2 套 BMI 生长图表。第一套显示了每个 GA 组中所有 5 个百分位组的拟合中位数曲线。第二套显示了按百分位组、GA 和性别分类的拟合中位数曲线及其相应的第三和 97 个百分位曲线。在验证分析中，中位数曲线以下的每日观察百分比在最初 3 天后接近预期的第 50 个百分位。与横断面曲线不同，纵向曲线揭示了与最低点相对应的变化模式；最低点过后，这些曲线一直低于横断面曲线，并且与 GA 和性别预期一致。横断面曲线（显示最佳生长）的观察百分比低于第 50 个百分位（显示实际生长）的情况通常远高于纵向曲线。
这些新的纵向曲线为临床医生提供了有关早产儿身体比例随时间变化的数据。
