Association between Growth Trajectories and Body Composition Outcomes in Very Preterm Infants: A Cohort Study

Introduction: There is a need to establish realistic, rather than idealistic, postnatal growth targets. We aimed to characterize body composition outcomes of preterm infants growing along recently defined individualized growth trajectories. Methods: In this cohort study, infants born <33 weeks of gestation in the United States, Canada, Germany, and Austria between 2012-2022 were included if they had body composition measurements at term-equivalent age. Growth trajectories for each infant were generated retrospectively based on weight data collected at birth and at term-equivalent age. This allowed for the calculation of the difference between actual and target weight at term-equivalent age or discharge and stratification of infants into three growth trajectories: 1) 100g or further below target, 2) within target (±99g), and 3) 100g or more above target. Results: A total of 1052 infants were included. The median gestational age and birthweight were 28 weeks and 1060g, respectively. A linear correlation between the actual versus target weight difference and fat-free mass (FFM) z-scores was found (r = 0.34, p < 0.0001). Among infants whose weights remained within the target range (30%), the mean FFM z-score was -1.6 [SD: 1.2] and the mean body fat percentage was 15 [SD: 5.9]. In addition to lower mean FFM z-scores, infants whose weight fell below the target range had greater declines in weight, length, and head circumference z-scores. Conclusions: Weight trajectories below a recently defined target is linked to lower FFM. Further research is needed to determine whether prospectively targeting these individualized growth trajectories improves FFM outcomes.