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

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.

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.

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.

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.