Birth-size reference charts for normal nursery newborns between 35 and 41 weeks

Objective Current birth-size reference charts for nursery use may inaccurately categorize newborn size, impacting care. We aimed to develop new charts using data from uncomplicated newborns admitted to US nurseries. Study Design We analyzed de-identified data from newborns admitted to US normal newborn nurseries between 2021 and 2024. Statistical outliers were excluded, and gestational age was recorded in days. Birth-size weight, length, head circumference ,and BMI models were developed by a randomly selected subset and validated by the remaining data. Proportions of small and large for gestational age (S/LGA) newborns were compared to the 2010 Olsen and 2013 Fenton charts. Results 129,150 uncomplicated newborns at 35–41 weeks of gestation were included. The new charts did not exhibit overfitting bias and more accurately identified the expected 10% of newborns as S/LGA compared to existing charts. Conclusion New charts (weight, length, head circumference, BMI) improve birth size referencing in normal newborn nurseries.