Clinical Validation of the INTERGROWTH-21st Standards of Fetal Abdominal Circumference for the Prediction of Small-for-Gestational-Age Neonates in Italy

Objectives: To compare the accuracy of the INTERGROWTH-21st (IG-21) with the Italian Society of Ultrasound in Obstetrics and Gynecology (SIEOG) abdominal circumference (AC) standards in the detection of small-for-gestational-age (SGA) fetuses in a high-risk population. Material and Methods: Our study included all pregnant patients with an increased risk of placental insufficiency that were seen in two Italian university hospitals between 2014 and 2015. The accuracy of IG-21 and SIEOG AC standards in the detection of SGA neonates was analyzed by means of the area under the receiver operating characteristic curve (ROC-AUC) at 4 gestational age intervals (24-27, 28-31, 32-35, >35 weeks). Results: We enrolled 428 patients (278 Italians). There was no significant difference between the ROC-AUC of AC according to IG-21 and SIEOG standards for all birthweight thresholds and gestational intervals that were considered. The diagnostic performance was similar in Italian and non-Italian patients. The accuracy was, however, limited, with values of ROC-AUC ranging between 0.80 and 0.89. Conclusions: The IG-21 and SIEOG AC standards are interchangeable for the diagnosis of SGA fetuses. The diagnostic accuracy is, however, limited. We provide figures that can be used to stratify the probability that an infant will be SGA in an obstetric population at increased risk of growth restriction.