2.Department of Medical Ultrasound, Wuxi People’s Hospital of Nanjing Medical University,Wuxi China#$NL ：Objective To validate the use of fractional limb volume obtained with 3D ultrasound for predicting late-onset fetal growth restriction (FGR) at 23-24 weeks of gestation by comparing with conventional 2D ultrasound. Methods A total of 74 pregnant women diagnosed with late-onset FGR in our hospital from January 2018 to December 2019 were selected into the case group, and 200 normal pregnant women were included as the control group. Measurements were performed at 23-24 weeks of gestation using 2D ultrasound for standard fetal biometry (double parietal diameter, head circumference, abdominal circumference, femur length and ultrasound-estimated fetal weights (EFW)), and 3D ultrasound for fractional arm volume (AVol) on 50% of the humeral diaphysis length and fractional thigh volume (TVol) on 50% of the femoral diaphysis length. The resulting areas under the ROC curves (AUC) were compared the parameters of the two groups for predicting the late-onset FGR. Results There were no significant differences in terms of double parietal diameter, head circumference, abdominal circumference, femur length and EFW, and statistically differences in AVol and TVol between the two groups. ROC analysis showed that the AUC values in predicting by AVol and TVol for late-onset FGR was 0.70 and 0.74, respectively. No significant differences were found between groups. The optimal cutoff values were 4.5 mL and 9.4 mL, respectively. The sensitivity, specificity and accuracy of predicting late-onset FGR of the two groups were 63.5% and 69.4%, 89.4% and 88.1%, 81.4%, and 83.2%, respectively. The sensitivity, specificity and accuracy in combined prediction of late-onset FGR were 79.0%, 94.8%, and 90.1%, respectively. Conclusions Fractional limb volume (AVol and TVol) assessment may improve the late-onset FGR prediction at 23-24 weeks of gestation.