Background: Current growth charts provide no target for how a preterm infant should grow. They also ignore the physiological postnatal adaptation to extrauterine life and weight loss in preterm and term infants. This weight loss is a one-time, irreversible, physiologic phenomenon. Recently we have studied the weight loss and downshifts of the postnatal growth trajectories during the first 21 days of life in healthy preterm infants and can be described precisely by a prediction model. However, the individual growth trajectory between day of life 21 and term, when preterm infants should achieve a weight and body composition similar to their term-equivalent, remains unclear. The aim of the study is to compare different approaches to create individualized postnatal growth trajectories for the period between birth and 42 + 0/7 weeks PMA, that consider the physiologic weight loss. Methods: Three approaches to achieve growth similar to healthy term infants at 42 + 0/7weeks PMA on WHO growth standards (target weight) were tested for infants born at 24-34 weeks PMA and for birth weights at 7 major percentiles. The three approaches include: 1) following the birth percentile (Birth-Weight-Percen-tile Approach), 2) following the new percentile achieved at DOL 21 after postnatal weight loss (Postnatal-Percentile Approach); 3) using day-specific fetal median growth velocities starting at DOL 21 (Growth-Velocity Approach). Primary outcome was the difference between achieved and target weight at 42 + 0/7 weeks. Secondary outcome was the deviation from target weights vs. % fat in a cohort of 20 disease-free VLBW infants. Results: The weights following the Birth-Weight-Percentile and Postnatal-Percentile approaches deviated significantly from target weights. Weights using the Growth-Velocity approach merged with the target weights after introducing a single correction factor. %fat and deviation from target weight correlated best with term equivalent %fat using the Growth-Velocity approach. The figure demonstrates an individualized growth trajectory using the Growth-Velocity approach for a male pre-term, born at 31 + 0/7 weeks, with a birth weight of 1980g. Conclusions: The Growth-Velocity approach provides an evidence-based approach for individualized growth trajectories. The Growth-Velocity approach is based on physiological data incorporating that phenomenon that healthy preterm infants adjust their postnatal trajectory below their birth percentile. After postnatal adjustment, the Growth-Velocity Approach applies the median fetal growth velocity. The Growth-Velocity approach matches consistently with term-equivalent weights at 42 + 0/7weeks. The Growth-Velocity approach has been integrated into a bedside tool that can be used to aid clinicians in monitoring growth, guiding nutrition and minimizing chronic adult disease risks (DOHaD) as a consequence of unguided, inappropriate growth.
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