Background: Low birth weight is associated with childhood stunting, but equivalent associations for birth body composition (BC) remain unknown.

Objective: To assess associations of BC with height-for-age Z score (HAZ) at 2 years of age.

Methods: In a prospective cohort study, fat mass (FM) and fat-free mass (FFM) were measured using air-displacement plethysmography within 48 h of birth. Linear regression models were applied to study the relationship between BC at birth and HAZ at 24 months (±3 months).

Results: A total of 268 children with height assessment at 2 years were included. Mean±s.d. HAZ at 2 years of age was -1.2±1.2, with 25.8% classified as stunted (HAZ<-2 s.d.). FFM at birth was positively associated with HAZ at 2 years, independent of length at birth. When adjusted for potential confounders, HAZ at 2 years was 0.73 higher for each additional kg FFM at birth (β=0.73, 95%CI (0.08, 1.38). FM was not associated with HAZ at 2 years in any model.

Conclusion: The FFM component of birth weight, independent of length, explains variability in HAZ at 2 years. Further studies are required to explore how changes in early infant BC are associated with linear growth.Pediatric Research accepted article preview online, 19 April 2017. doi:10.1038/pr.2017.59.