Background and Objectives: Infants experiencing catch-up growth devote a greater proportion of their energy to fat deposition, potentially at the expense of gains in lean body mass. The objective of the present study was to compare the body composition of preterm and term infants after hospital discharge and to determine the effect of gestational age (GA), birth size, nutrition, and illness on growth in fat-free mass (FFM) after hospitalization.
Patients and Methods: Anthropometric measurements and body composition testing via air displacement plethysmography were performed on 26 appropriate-for-gestational-age (AGA) preterm (mean GA 31.5 ± 2.7 weeks) and 97 AGA term (mean GA 39.8 ± 1.0 weeks) infants at term corrected age (CA) and at 3 to 4 months CA.
Results: At term CA, preterm infants had lower FFM (3.0 vs 3.3 kg, P = 0.001), higher percentage of body fat (18.7% vs 15.2%, P < 0.0001), lower weight (P = 0.04), and shorter length (P = 0.001) than term infants. By 3 to 4 months CA, weight, length, percentage of body fat, and FFM were similar in the 2 groups. GA, inpatient nutrition, and illness were associated with FFM at 4 months CA in the preterm infants (P < 0.05).
Conclusions: Markedly lower FFM and higher adiposity were observed in preterm infants at term CA, but these differences had lessened and were no longer statistically significant at 3 to 4 months CA. Although early nutrition was associated with growth trajectories in the hospital, the continuing influence of early illness on postdischarge growth suggests that nonnutritional factors (eg, disturbances in the growth hormone axis) also may affect body composition trajectories of preterm infants.