New body composition reference charts for preterm infants

Background: The American Academy of Pediatrics (AAP) has recommended that nutritional management of the preterm infant should aim to achieve body composition that replicates the in utero fetus, but intrauterine body composition reference charts for preterm infants are lacking. Objective: Our objective was to create body composition reference curves for preterm infants that approximate the body composition of the in utero fetus from 30–36 weeks gestation. Design: 223 ethnically diverse infants born at 30+0 to 36+6 weeks gestation were enrolled. Inclusion/exclusion criteria were specified so that the sample would represent healthy appropriately growing fetuses (e.g., singleton, birth weight appropriate for their gestational age, medically stable). Cross-sectional reference values were generated for fat mass (FM), fat-free mass (FFM), and percent body fat (PBF) by gestational age, using air displacement plethysmography (ADP) and the LMS (lambda-mu-sigma) method for percentile estimation. Results: Gestational-age specific percentile values and a percentile and z score calculator for FFM, FM, and PBF are presented. These values aligned closely with ADP centile values published for term infants from 36-38 weeks gestation. The medians were also similar to the mean values for the reference fetus derived from chemical analysis previously. Conclusions: These are the first body composition reference charts for total body fat and fat-free mass at birth in preterm infants to assist in following AAP guidelines. Future work will test the clinical utility of body composition monitoring for improving nutritional management in this population.