Objective Recently, a Delphi procedure was used to establish new criteria for defining fetal growth restriction (FGR). These criteria require clinical validation. We sought to validate the Delphi consensus criteria by comparing their performance with that of our current definition (estimated fetal weight (EFW) < 10th percentile) in predicting adverse neonatal outcome (ANO). Methods This was a secondary analysis of data from a prospective cohort study of women referred for fetal growth assessment between 26 and 36 weeks' gestation. The current standard definition of FGR used in our clinical practice is EFW < 10th percentile using Hadlock's fetal growth standard. The Delphi consensus criteria for FGR include either a very small fetus (abdominal circumference (AC) or EFW < 3rd percentile) or a small fetus (AC or EFW < 10th percentile) with additional abnormal Doppler findings or a decrease in AC or EFW by two quartiles or more. The primary outcome was the prediction of a composite of ANO including one or more of: admission to the neonatal intensive care unit, cord pH < 7.1, 5‐min Apgar score < 7, respiratory distress syndrome, intraventricular hemorrhage, neonatal seizures or neonatal death. The discriminatory capacities of the two definitions of FGR for composite ANO and delivery of a small‐for‐gestational‐age (SGA) neonate, defined as birth weight < 10th percentile, were compared using area under the receiver‐operating‐characteristics curve (AUC). The sensitivity, specificity and predictive values of the methods were also compared. Results Of 1055 pregnancies included in the study, composite ANO occurred in 139 (13.2%). There were only two cases of early FGR (before 32 weeks); therefore, the study focused on late FGR. Our current FGR diagnostic criterion of EFW < 10th percentile was not associated significantly with composite ANO (relative risk (RR), 1.1 (95% CI, 0.6–1.8)), while the Delphi FGR criteria were (RR, 2.0 (95% CI, 1.2–3.3)). Our current definition of FGR showed higher discriminatory ability in the prediction of a SGA neonate (AUC, 0.69 (95% CI, 0.65–0.73)) than did the Delphi definition (AUC, 0.64 (95% CI, 0.60–0.67)) (P = 0.001). The AUCs of both definitions were poor for the prediction of composite ANO, despite slightly improved performance using the Delphi consensus definition of FGR (AUC, 0.53 (95% CI, 0.50–0.55)) compared with that of our current definition (AUC, 0.50 (95% CI, 0.48–0.53)) (P = 0.02). Conclusion The newly postulated criteria for defining FGR based on a Delphi procedure detects fewer cases of neonatal SGA than does our current definition of EFW < 10th percentile, but is associated with a slight improvement in predicting ANO. Copyright © 2020 ISUOG. Published by John Wiley & Sons Ltd.

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