Differences in Body Composition and Energy Expenditure in Prepubertal Children Born Term or Preterm Appropriate or Small for Gestational Age

Small size at birth may result from fetal undernutrition which may occur at different times during gestation. Early postnatal catch-up growth and excess childhood weight gain are associated with an increased risk of adult cardiovascular disease and type 2 diabetes mellitus. The aim of this study was to assess the relative contributions of body composition and energy expenditure on fasting insulin sensitivity during late childhood. We took, advantage of two previously described prospective cohorts of children born either at term or prematurely, with a wide range of birth weights adjusted for gestational age. Seventy-one prepubertal children (mean age 7.5 +/- 0.3 years) were examined: 23 term SGA (8 M, 15 F), 12 preterm SGA (7 M, 5 F), 16 term AGA (8 M, 8 F), and 20 preterm AGA (9 M, 11 F). Mean height SDS was -0.18 +/- 0.11 and mean BMI SDS was 0.27 +/- 0.03. Change in weight SDS was significantly higher in children born SGA compared to their AGA counterparts (p <0.001). Change in weight SDS was highly correlated with fasting insulin (p <0.03) and leptin (p <0.001). Fasting insulin correlated only with serum leptin levels. Body composition appeared to be the main determinant of fasting leptin levels. No differences in lipid profile were observed between the different groups. There was a clear tendency to higher insulin and leptin levels in children born SGA compared with their AGA counterparts. IGF-I levels were significantly higher only in SGA term compared to AGA term. Resting energy expenditure (REE) was lower in SGA horn at term and higher in SGA born preterm compared to their AGA counterparts. In conclusion, fasting insulin sensitivity is mainly determined by leptin levels which in turn are determined by body composition. IGF-I and REE showed a divergent pattern in SGA term compared to SGA preterm groups. IGF-I levels were determined only by weight change from birth to age 2 years, which may not be as pronounced in VLBW children compared to SGA term and thus may preclude a difference in IGF-I levels in the group of preterm children. The divergent effect in REE in SGA born at term compared to SGA born preterm compared to their AGA counterparts may explain the divergent effects on IGF-I. This difference might be a consequence of different timing in the exposure to intrauterine nutritional deficiency.