'Peas in a Pod?' - The body composition of the term and preterm infant

Abstract

Introduction: Weight has been the primary outcome measure for many studies of both term and preterm infants. Body composition reflects the quality of infant growth. Using air displacement plethysmography, infant body composition can now be measured longitudinally both safely and accurately. The aim of the study was to describe and compare changes in body fat percentage in term and preterm infants in early infancy and factors which may affect this. Methods: Term infants (37-42 weeks) from the postnatal ward and preterm infants (<37 weeks) who required admission to the neonatal unit were recruited to the study. Term infants had anthropometry and body composition measured at birth and 4 months of age. Preterm infants had anthropometry and body composition measured at 35 weeks corrected gestational age (CGA), term corrected age (TCA), 6 weeks and 4 months CGA. Information with regard to maternal body mass index, gestational diabetes, smoking status, infant gestation, gender and mode of feeding was collected. Results: 374 term infants were measured before 72 hours of life and 460 term infants were measured at 4 months of whom 248 had body composition measurements performed. Term male infants were heavier with lower body fat percentage than female infants. Maternal BMI had a statistically significant but clinically insignificant effect on birth weight and neonatal body fat percentage.195 preterm infants had measurements. Mean gestation at birth and birth weight was 32.4 weeks and 1.83kg respectively. 174 preterm infants had measurements performed at TCA (130 body composition).163 preterm infants had measurements performed at a mean of 6.3 weeks CGA (100 body composition). Measurements were available for 136 preterm infants at 4 months CGA (43 body composition). Unlike infants born at full term, there was no difference in mean body fat percentage between preterm male and female infants. At TCA mean body fat percentage was higher in preterm infants than term infants, however at 4 months CGA no difference was observed. Discussion and Conclusions: There are rapid changes in body composition in early life on which maternal BMI has a small effect. This raises the possibility of a window in which to intervene in the prevention of obesity. Despite many years of research into the nutrition of preterm infants, they do not grow and accumulate body fat in the same way as term infants. The lack of gender difference in body fat percentage observed in preterm infants is concerning for the lifelong cardiovascular health of male preterm infants. Questions about long term body composition remain.