Total energy expenditure, body composition and weight gain in moderately preterm and full-term infants at term postconceptional age

Aim: To assess total energy expenditure (TEE) and body composition, i.e. total body water (TBW) and adipose tissue volume (ATV), at term age in 8 healthy preterm infants, born between gestational weeks 30 and 33, and in 9 healthy full-term newborns. Methods: Total and subcutaneous ATVs were assessed using magnetic resonance imaging, while TEE and TBW were estimated using doubly labelled water. Results: Total ATV was 272 +/- 21 and 261 +/- 56 ml/kg body weight, while subcutaneous ATV was 88.9 +/- 1.6 and 89.7 +/- 2.0% of total ATV for preterm and full-term infants, respectively. The corresponding figures for TBW (as percentage of body weight) were 67.4 +/- 2.5 and 68.1 +/- 4.1, respectively. A significant correlation between ATV/kg body weight and body weight was found for full-term (p < 0.0001) but not for preterm infants. TEE for preterm infants was 315 +/- 20 kJ/kg body weight/24 h, which was significantly higher (p < 0.05) than TEE for full-term infants (254 +/- 45 kJ/kg body weight/24 h). At the time of investigation preterm infants weighed significantly (p < 0.05) less (540 g) than full-term infants. After the time of investigation, weight gains of preterm and full-term infants were 38 +/- 12 and 24 +/- 14 g/24 h, respectively. Conclusion: When compared to full-term newborns, predominantly breastfed healthy preterm infants at term postconceptional age were significantly smaller, had a similar average proportion of body fat and showed catch-up growth. Their higher TEE/kg body weight can be explained by a higher growth rate and possibly also by higher physical activity.