541A Nationwide Evaluation of International Standards and Commonly-used Growth Charts for Predicting Adverse Perinatal Outcomes

Background Abnormal fetal growth is a risk factor for perinatal mortality and morbidity. There is considerable debate about the choice and performance of growth charts to classify newborns as small or large for gestational age (SGA and LGA) as a proxy for the at-risk infants. Several international charts have been proposed to be adopted worldwide. We aim to evaluate the performance of commonly-used growth charts (including international INTERGROWTH-21st-standards) for predicting adverse outcomes among SGA and LGA babies. Methods A population cohort of 2.4 million singleton births (24+0–40+6 weeks) delivered in Australia, 2004–2013. Performance was evaluated by prevalence, relative risk and diagnostic accuracy for adverse outcome based on AUC. Results There was wide variation in SGA and LGA classification across charts. For example, compared to other charts, the INTERGROWTH-21st-standards classified half of the number of term-SGA babies (prevalence: 3-4% vs. 7-10%) (90th-centile), resulting in a smaller cohort of term-SGA at higher-risk of adverse outcome, and a larger LGA cohort with lower-risk of adverse outcome. All charts performed poorly for detecting adverse outcomes (AUC range for a composite outcome: 0.49-0.68) and across birthweight centiles. Conclusions Significant differences in the classification of newborns and the chart performance raises concerns about whether the INTERGROWTH-21st-standards are applicable to a multi-ethnic population such as Australia. Key messages Significant differences in the classification of newborns and the relatively poor predictive ability of growth charts means that over reliance on infant size alone may misclassify, and thus miss at-risk infants.