P2C336: Predictors of Postnatal Growth in a Late Preterm Population

Background: The early postnatal period is an important time of growth and rapid fat mass accrual, especially for late preterm infants. The optimal growth trajectory in this population is unknown; while adequate growth is desired, rapid growth in early infancy is a risk factor for obesity in childhood. This study aims to describe the growth trajectory over the first 6 months of life and associated maternal and infant factors for infants born at 35/0-36/6 weeks gestation.

Methods: A retrospective chart review was performed on healthy infants 35/0-36/6 weeks gestation born at the University of Michigan between 2016-2022 including infants born at a weight appropriate for gestational age (10-90th percentile) or small for gestational age ( < 10th percentile) (N=590). Infant weight, length, and weight-for-length measurements were reviewed at birth and near 6 months of age, based on documented measurements in the electronic health record from clinic visits. Z-scores were determined using Fenton and World Health Organization (WHO) growth charts. Maternal and infant records were reviewed for birth history, demographics, maternal metabolic disease, and mode of feeding. Multivariate regression analysis was used to evaluate the associations of maternal/infant characteristics with change in weight-for-age (WFA) Z-score, length-for-age (LFA) Z-score, weight-for-length (WFL) Z-score, and rapid infant weight gain (change in WFA Z-score >0.67 SDS).

Results: Our cohort included 590 infants with average gestational age of 36/1 weeks. This included 147 infants with rapid postnatal growth (change in WFA Z-score >0.67 SDS), 309 infants with normal postnatal growth (change in WFA Z-score between -0.67 and +0.67 SDS), and 134 infants with slow postnatal growth (change in WFA Z-score <-0.67 SDS). Change in WFA Z-score from birth to 6 months was associated with maternal diabetes (β -0.33, CI -0.53 – -0.12) and formula-feeding at 6 months of age (β 0.43, CI 0.24 – 0.63). Change in LFA Z-score from birth to 6 months was associated with gestational age (β -0.55, CI -0.74 – -0.36) and formula-feeding at 6 months of age (β 0.54, CI 0.29 – 0.80). Change in WFL Z-score from birth to 6 months was associated with maternal diabetes (β -0.48, CI -0.82 – -0.14). Rapid infant weight gain was associated with maternal diabetes (OR 2.08, CI 1.25 – 3.46). Additionally, race and ethnicity were associated with infant growth trajectories.

Conclusion: Changes in postnatal growth measurements between birth and 6 months of age were associated with maternal diabetes, feeding method, and race and ethnicity. These findings suggest modifiable and non-modifiable factors as predictors of postnatal growth in the high risk late preterm population for which future interventions could be applied.