Relationship of Anthropometric and Biochemical Measurements with Body Fat Content for the Evaluation of the Nutritional Status of Preterm Infants

Presenter: John Ladino (e-mail: [e-mail])

Introduction: Preterm infants are at risk of developmental delays and metabolic sequelae as a result of inadequate growth. Body mass index (BMI), ponderal index (PI), and air-displacement plethysmography (ADP) have been used to assess the nutritional status of the newborn. While BMI and PI are easy to perform, ADP is time consuming and it is not always technically feasible. It is not known if BMI and PI correlate with measurements of body fat content obtained by ADP in preterm (PT) infants. Similarly, blood urea nitrogen (BUN) has been used as an index to evaluate protein metabolism after birth. The possible relation between body fat content and BUN values while on enteral feeds has not been completely elucidated. Our objectives are to evaluate the relationship between percentage body fat (%BF) and BMI, PI, and BUN in PT infants.

Materials and Methods: This is an observational case series study including 133 PT infants born at 24 to 32 weeks with no chromosomal/metabolic anomalies and on full feeds as per the feeding protocol at time of measurement. When clinically stable, measurements of %BF by ADP (Pea Pod, Cosmed), weight, and length were performed (364 sets of values included). Values of BUN performed 5 days before or after ADP measurements were also recorded for 95 infants. Descriptive and comparative statistics were analyzed and correlation values for %BF and BMI, PI, or BUN are reported.

Results: Our analysis found a strong correlation between %BF and BMI (see Fig. 1). However, no correlation was found between serum BUN concentration and body fat content. We speculate that BMI can be used to monitor growth, particularly fat content, if methods such as ADP are contraindicated or not available. This will facilitate the application of timely and appropriate nutritional interventions for premature infants admitted to the NICU.

Conclusion: Our results also suggest that BUN may not be an adequate index of protein metabolism in the newborn.

Keywords: body fat content, body mass index, blood urea nitrogen, preterm

Fig. 1 Relationship between percentage body fat (%BF) and body mass index (BMI) in the studied preterm infants.