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Updated: Mar 15, 2026
Assessment of Child Anthropometry in a Large Epidemiologic Study
Published on: February 2, 2017
Do anthropometric measures accurately reflect body composition in preterm infants?
S E Ramel1, L Zhang2, S Misra3
1Department of Pediatrics, University of Minnesota, Minneapolis, MN, USA.
Insights
Weight is a good indicator of lean mass in preterm infants, but standard weight-to-length ratios do not accurately measure body fat. These indices are not suitable for assessing adiposity in newborns.
Area of Science:
- Neonatal physiology
- Pediatric nutrition
- Body composition analysis
Background:
- Neonatal adiposity and lean mass predict later metabolic and cognitive health, respectively, in preterm infants.
- Accurate anthropometric indices for neonatal body composition are needed for clinical care and research.
- Existing indices have not been systematically validated in preterm infants.
Purpose of the Study:
- To identify the most effective weight/length indices for assessing neonatal body composition in preterm infants.
- To evaluate the validity of anthropometric proxies for fat-free mass (FFM), fat mass (FM), and percent body fat (%BF) at birth.
Main Methods:
- 218 preterm infants had body composition (FFM, FM, %BF) measured via air-displacement plethysmography within 72 hours of birth.
- Weight and length were recorded.
- Linear regression models assessed weight/length indices, using variance explained (R² ) and root mean square error (RMSE) to determine the best proxies.
Main Results:
- Body weight alone was a strong predictor of FFM (R² =0.97).
- Weight/length² was the best proxy for %BF, but explained little variance (R² =0.27) and had high prediction error (RMSE=3.5% fat).
- No tested weight/length index accurately reflected %BF.
Conclusions:
- Weight/length indices are unsuitable for assessing relative adiposity in preterm infants at birth.
- Body weight is an adequate surrogate for lean mass in preterm neonates.
- Further research is needed to establish reliable methods for assessing adiposity in preterm infants.
Background:
Recent literature suggests that neonatal adiposity is predictive of later metabolic health, while neonatal lean mass is predictive of later cognitive function amongst preterm infants. Anthropometric indices that accurately reflect neonatal body composition could improve clinical care and aid future research, but their validity has not been systematically tested in preterm infants.
Objective:
To determine the weight/length indices that best reflect neonatal body composition in preterm infants.
Methods:
Weight and length were measured, and body composition (fat-free mass (FFM), fat mass (FM) and percent body fat (%BF)) was assessed using air-displacement plethysmography within 72 h of birth in 218 preterm infants. The best weight/length proxy for FFM, FM and %BF were those with the highest proportion variance explained (R2 ) and lowest root mean square error (RMSE) in linear regression models.
Results:
Among all of the weight/length indices tested, weight/length2 was the best proxy for %BF, but nonetheless exhibited very low variance explained (R2 = 0.27) and high prediction error (RMSE = 3.5% fat). Body weight unadjusted for length was strongly associated with FFM (R2 = 0.97).
Conclusions:
No weight/length index accurately reflected %BF. Weight/length indices are not appropriate for assessment of relative adiposity in preterm infants near birth. What's known on this subject: Compared with term infants, preterm infants have increased fat mass and diminished fat-free mass upon hospital discharge. Early adiposity predicts later metabolic health, while early lean mass is predictive of later neurodevelopmental outcomes. Optimal anthropometric proxies for preterm body composition at birth are not established.
What This Study Adds:
Weight is an adequate surrogate for lean mass at birth in preterm infants. There are no weight/length indices that accurately reflect neonatal adiposity at birth.
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