DXA-Derived Body Composition and Insulin Resistance at Preschool Age in Very-Low-Birth-Weight Preterm Infants: A Prospective Cohort Study

Background/Objectives: Preterm infants have higher fat mass and lower lean mass at term-corrected age; however, whether these differences persist into preschool age remains unclear. This prospective observational cohort study aimed to compare body composition between very-low-birth-weight (VLBW) preterm (gestational age < 33 weeks) children and their term-born counterparts aged 5–6 years. Methods: Anthropometric data, body composition, blood biochemical parameters, and insulin resistance (HOMA-IR index) were compared between the preterm and term groups. Results: The study included 96 children (57 preterm and 39 term-born). Although lean mass index and fat mass index were comparable between groups, preterm children exhibited significantly higher insulin levels and HOMA-IR values after adjustment (p = 0.003 and p = 0.004, respectively). Within the preterm cohort, overweight/obesity was associated with higher trunk and total fat percentages, as well as higher HOMA-IR, compared with those of normal-weight or underweight children (all adjusted p < 0.001). Weight growth velocity from 2 to 5 years was positively associated with serum insulin, HOMA-IR, and both trunk and total body fat percentages. Additionally, girls in both groups displayed significantly higher trunk and total body fat percentages than boys. Conclusions: Children born very preterm with VLBW had higher fasting insulin levels and HOMA-IR, despite generally comparable DXA-derived LMI, FMI, and fat distribution at preschool age. Overweight status and rapid early childhood weight gain may contribute to increased metabolic risk in this population, highlighting the need for early metabolic monitoring and growth management. Future large-scale, long-term studies are required to confirm these findings.