Early weight gain trajectories and body composition in infancy in infants born very preterm

Background Concerns are raised about the influence of rapid growth on excessive fat mass (FM) gain in early life and later cardiometabolic health of infants born preterm. Objectives To study the association between postnatal weight gain trajectories and body composition in infancy in infants born very preterm. Methods In infants born <30 weeks gestation, we evaluated associations between weight Z-score trajectories for three consecutive timeframes (NICU stay, level-II hospital stay and at home) and body composition, measured at 2 and 6 months corrected age by air-displacement plethysmography. Results Of 120 infants included, median gestational age at birth was 27(+5) (interquartile range 26(+1);28(+5)) and birth weight 1015 g (801;1250). The majority of infants did not make up for their initial loss of weight Z-score, but growth and later body composition were within term reference values. Weight gain during NICU stay was not associated with fat mass (absolute, %FM or FM index) in infancy. Weight gain during NICU and level II hospital stay was weakly associated with higher absolute lean mass (LM), but not after adjustment for length (LM index). Weight gain in the level-II hospital was positively associated with fat mass parameters at 2 months but not at 6 months. Strongest associations were found between weight gain at home and body composition (at both time points), especially fat mass. Conclusions Weight gain in different timeframes after preterm birth is associated with distinct parameters of body composition in infancy, with weight gain at home being most strongly related to fat mass.