Comparison of SGA and Severe SGA rates using six size standards – Is there a difference?

•Different growth standards lead to significantly different rates of SGA and severe SGA diagnoses.•Choosing a growth standard suited to the local population is crucial for accurate diagnosis.•Overdiagnosis and underdiagnosis of SGA can both have negative consequences. Small for gestational age (SGA) neonates are known to be at an elevated risk for neonatal morbidity. Despite this, there is a growing array of proposed size standards for identifying SGA fetuses. Given the inherent differences in design, acquisition methods, and the characteristics of the populations they represent, the generalizability of these standards to diverse populations remains uncertain. This study aimed to assess variations in rates of SGA and severe SGA using six distinct size standards: Hadlock, Fetal Medicine Foundation (FMF), World Health Organization (WHO), Intergrowth-21 (IG-21), and two locally derived population-based size standards. The objective was to examine the differences in SGA and severe SGA rates among these size standards. A retrospective cohort study was conducted, encompassing all singleton deliveries in two tertiary referral hospital campuses with an annual birth count exceeding 10,000, from January 2019 to July 2022. SGA and severe SGA were defined as birthweights below the 10th or 3rd percentile, respectively, based on each growth standard. The study design included details on the setting, subjects (singleton deliveries), and the chosen size standards. Comparative analyses were performed to assess variations in SGA and severe SGA rates among these size standards. Our study analyzed 32,912 singleton deliveries. We found that the choice of growth standard significantly impacted the rates of both SGA and severe SGA infants. Notably, the WHO criteria identified 5,548 (16.9 %) fetuses as SGA, compared to only 1,716 (5.2 %) using the INTERGROWTH-21 standard (p