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BMI Is a Better Body Proportionality Measure than the Ponderal Index and Weight-for-Length for Preterm Infants
A Nicole Ferguson1, Shannon C Grabich, Irene E Olsen
1Department of Statistics and Analytical Sciences, Kennesaw State University, Kennesaw, GA, USA.
Insights
Body Mass Index (BMI) is the best measure for assessing preterm infant growth proportionality, outperforming the ponderal index. This finding is crucial for accurate neonatal intensive care unit assessments.
Area of Science:
- Neonatalogy
- Pediatric Growth Assessment
- Body Composition Analysis
Background:
- Clinicians observe disproportionate growth in preterm infants in neonatal intensive care units.
- Existing growth charts rely on outdated data from the 1950s using the ponderal index.
- Limited evidence supports the ponderal index for modern preterm infant growth assessment.
Purpose of the Study:
- To identify the optimal measure of body proportionality for evaluating growth in US preterm infants.
- To establish evidence-based growth assessment tools for neonatal intensive care.
Main Methods:
- Analysis of a large dataset (391,681 infants) to determine body proportionality measures.
- Examination of correlations between measures, weight, and length, stratified by sex and gestational age.
- Visualization of body proportionality measures against infant length to identify discrepancies.
Main Results:
- Overall, the ponderal index (weight/length³) showed the highest correlation with weight.
- Stratification by gestational age revealed Body Mass Index (BMI, weight/length²) as the superior measure.
- BMI demonstrated appropriate correlation with length across gestational ages, unlike the ponderal index.
Conclusions:
- Body Mass Index (BMI) is the recommended measure for assessing body proportionality in preterm infants.
- Current reliance on the ponderal index for preterm infant growth assessment is suboptimal.
- Updated growth assessment standards are needed for neonatal intensive care units.
Background:
Clinicians have observed preterm infants in the neonatal intensive care unit growing disproportionally; however, the only growth charts that have been available were from preterm infants born in the 1950s which utilized the ponderal index. Prior to creating the recently published BMI curves, we found only 1 reference justifying the use of the ponderal index.
Objectives:
To determine the best measure of body proportionality for assessing growth in US preterm infants.
Methods:
Using a dataset of 391,681 infants, we determined the body proportionality measure that was most correlated with weight and least correlated with length. We examined the sex-specific overall correlations and then stratified further by gestational age (GA). We then plotted the body proportionality measures versus length to visualize apparent discrepancies in the appropriate measure.
Results:
The overall correlations showed weight/length3 (ponderal index) was the best measure but stratification by GA indicated that BMI (weight/length2) was the best measure. This seeming inconsistency was due to negative correlations between ponderal index and length at each GA. BMI, on the other hand, had a correlation with length across GAs, but was uncorrelated with length within GAs. Both ponderal index and BMI were positively correlated with weight.
Conclusions:
BMI is the appropriate measure of body proportionality for preterm infants, contrary to current practice.
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