New charts for the assessment of body composition, according to air-displacement plethysmography, at birth and across the first six months of life

Background: Air-displacement plethysmography is a good candidate for monitoring body composition in new-borns and young infants, but reference centile curves are lacking that allow for assessment at birth and across the first six months of life. Objective: Using pooled data from four studies, we aimed to produce new charts for assessment according to gestational age at birth (30+1 to 41+6 weeks) and postnatal age at measurement (1 to 27 weeks). Design: The sample comprised 222 preterm infants born in the United States of America (USA) who were measured at birth; 1029 term infants born in Ireland who were measured at birth; 149 term infants born in the USA and 57 term infants born in Italy who were measured at birth, 1 & 2 weeks and 1, 2, 3, 4, 5, & 6 months of age. Infants whose birth weights were <3rd or >97th centile of the INTERGROWTH-21st standard were excluded, thereby ensuring that the charts depict body composition of infants whose birth weights did not indicate suboptimal fetal growth. Sex-specific centiles for fat mass (kg), fat-free mass (kg), and percentage body fat were estimated using the lambda-mu-sigma (LMS) method. Results: For each sex and measure (e.g., fat mass), the new charts comprise two panels. The first shows centiles according to gestational age, allowing term infants to be assessed at birth and preterm infants to be monitored until they reach term. The second shows centiles according to postnatal age, allowing all infants to be monitored to age 27 weeks. The LMS values underlying these charts are presented, enabling researchers and clinicians to convert measurements to centiles and Z-scores. Conclusions: These charts provide a single tool for the assessment of body composition, according to air-displacement plethysmography, in infants across the first six months of life and will help enhance early-life nutritional management.