Body composition at school age after very preterm birth: a cohort study

Objective To assess body composition in school-aged children born very preterm and examine its associations with gestational age, birthweight z-score and sex. Design Observational cohort study. Setting Single tertiary care centre (University Children’s Hospital, Tübingen, Germany). Patients Children born very preterm (<32 weeks’ gestation) aged 6–10 years. Main outcome measures Body fat percentage (BF%), fat mass (FM) and fat-free mass (FFM) were assessed by air displacement plethysmography. Fat mass index (FMI) and fat-free mass index (FFMI) were calculated. BF% and FFMI were considered the primary body composition outcomes. Results Among 237 children (median age 8.1 years), median BF% was 13.5% (IQR 9.1–18.4), FMI 1.95 kg/m² (1.27–2.89) and FFMI 12.88 kg/m² (12.14–13.60). In prespecified multivariable analyses, higher birth weight z-score was associated with higher BF% (B=1.26, 95% CI 0.13 to 2.39) but not with FFMI (B=0.17, 95% CI −0.02 to 0.35). Higher birth weight z-score was also associated with higher FM, FMI and FFM. Gestational age at birth was not independently associated with any body composition outcome. Female sex was associated with higher BF%, FM and FMI and with lower FFMI and FFM. Conclusions In children born very preterm, birthweight z-score, but not gestational age at birth, was independently associated with body composition at school age. These findings suggest that fetal growth may be more closely related to body composition at school age than the degree of prematurity itself.