Comparison of the Haksari newborn curve vs. the Fenton growth chart and INTERGROWTH-21st newborn size standards for classifying birthweight relative to gestational age: a report from a tertiary referral hospital in Indonesia

Birthweight-for-gestational-age classification is widely used to identify newborns at risk of adverse outcomes. International growth references, including the Fenton Growth Chart and the INTERGROWTH-21st Newborn Size Standards, are commonly used in clinical practice. However, the use of growth charts derived from external populations may result in different classifications. The Haksari Newborn Curve was developed from Indonesian birth data to provide an Indonesian population-specific reference. This study aimed to evaluate the agreement between Haksari and two international growth references in classifying birthweight-for-gestational-age. We conducted a cross-sectional study of singleton live-born infants without major congenital anomalies delivered at Academic Hospital Universitas Gadjah Mada, a tertiary referral hospital in Yogyakarta, Indonesia, between 2018 and 2025. Birthweight-for-gestational-age was classified as small (SGA), appropriate (AGA), or large (LGA). The main Haksari-Fenton comparison was restricted to preterm infants (< 37 completed weeks) to address the intended clinical population of Fenton, while the full-population analysis was presented as an exploratory analysis. The main Haksari-INTERGROWTH-21st comparison included the full study population. Agreement was assessed using observed agreement and weighted and unweighted Cohen’s kappa with 95% confidence intervals. Classification discordance was further evaluated according to gestational age and sex. A sensitivity analysis using exact gestational age was also performed. A total of 1395 newborns were included, of whom 54.1% were boys and 16.6% were preterm. Within the overlapping gestational-age ranges, the Haksari showed lower 10th and 90th percentile boundaries than the international references. The main preterm-restricted Haksari-Fenton comparison showed moderate agreement (weighted κ = 0.490; 95% CI 0.391–0.589; 28.1% discordance), whereas the exploratory full-population analysis showed fair agreement (weighted κ = 0.245; 95% CI 0.204–0.285; 33.8% discordance). The main Haksari-INTERGROWTH-21st comparison showed moderate agreement (weighted κ = 0.405; 95% CI 0.355–0.455; 22.6% discordance). Classification discordance remained evident at both the SGA and LGA thresholds. Birthweight-for-gestational-age classification differed between the Haksari and the two international growth references in this single-centre study. These findings suggest that the growth references are not interchangeable and may result in different clinical classifications. Further outcome-based studies in diverse Indonesian populations are needed before recommending any growth reference for routine clinical use. Not applicable.