Is Fat Mass Accretion of Late Preterm Infants Associated with Insulin Resistance?

Background: Late preterm infants show a major fat mass accretion from birth to term. The contribution of preterm birth to the development of the metabolic syndrome is still under investigation. Objectives: To evaluate body composition changes in late preterm infants during the first 3 months and to investigate their insulin sensitivity and resistance. Methods: We conducted an observational, longitudinal study. A total of 216 late preterm infants underwent body composition assessment using an air displacement plethysmograph at term and at 3 months of corrected age. In a subgroup of infants (n = 48) the blood glucose and insulin concentration were determined at term and insulin resistance (homeostasis model assessment for insulin resistance; HOMA-IR) and sensitivity (quantitative insulin sensitivity check index; QUICKI) were then calculated. The reference group comprised 71 healthy term infants. Results: The mean birth weight and gestational age were 2,390 ± 391 g and 35.2 ± 0.8 weeks, respectively. At term the fat mass index (kg/m²) of late preterm infants, born adequate for their gestational age and small for their gestational age, was higher than that of term infants (2.08 ± 0.82 vs. 1.62 ± 0.64 vs. 1.03 ± 0.36, p < 0.005, respectively), whereas at 3 months of corrected age no difference was found among the groups. The mean values of glucose, insulin, HOMA-IR, and QUICKI were within the 5th and 95th percentiles. Conclusions: On the basis of these preliminary findings, fat mass accretion of late preterm infants appears not to be associated with perturbation of the glucose homeostasis.