A Korean national birthweight reference for singleton live births

Objective: To develop a national birth weight reference for singleton live births in Korea using nationwide data, provide sex-specific percentile charts, and compare the Korean reference with widely used international birth weight references. Methods: Nationwide birth registration microdata for singleton live births between 2019 and 2023 were used. The data were obtained from Statistics Korea and accessed through the MicroData Integrated Service. Smoothed gestational age (GA)-specific birth weight percentile curves were generated overall and separately for male and female neonates. The Korean reference curves were compared with the United States national birth weight reference and INTERGROWTH-21st standards. Results: 1) A total of 1,158,083 singleton live births were included in the analysis. Smoothed GA-specific birth weight percentile curves were generated overall and separately for male and female neonates. 2) Male neonates had consistently higher birth weights than female neonates across GAs, with a median difference of approximately 100 g from the third trimester onward. And 3) the Korean national birth weight reference was compared with the United States national birth weight reference and the INTERGROWTH-21st standards. The United States national reference classified 66.6% of neonates classified as large for GA by the Korean reference as appropriate for GA, whereas INTERGROWTH-21st classified 65.6% of neonates classified as small for GA by the Korean reference as appropriate for GA. Conclusion: This study reports a nationwide Korean birth weight reference for singleton live births. The Korean birth weight reference differs from the widely used international references, supporting the need for population-specific charts for size assessment in Korean fetuses and neonates.