Birth-size reference charts for normal nursery newborns between 35.0 and 41.6 weeks

BACKGROUND: 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. METHODS: 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 weight, length, head circumference, and BMI models were developed by a randomly selected subset and validated by the remaining data. Proportions of newborns below the 10th percentile and above the 90th percentile were compared with the 2010 Olsen and 2013 Fenton charts. RESULTS: Uncomplicated newborns born between 35.0 and 41.6 weeks of gestation were included. The new charts did not exhibit overfitting bias and more accurately identified the expected 10% of newborns below the 10th and above the 90th percentiles compared to existing charts. CONCLUSIONS: New charts (weight, length, head circumference, BMI) improve birth-size referencing in normal newborn nurseries.