Abstract: Objective To investigate the clinical value of ultrasound blood flow parameters combined with peripheral blood growth arrest specific protein 6 (Gas6) in predicting fetal growth restriction (FGR) in the third trimester of pregnancy. 
Methods A total of 285 pregnant women in the third trimester who were registered in the hospital from Jan.to Dec. 2022 were selected as the research subjects. All pregnant women underwent ultrasound examination and peripheral blood Gas6 examination, and were followed up until the end of pregnancy. They were divided into the occurrence group and the non-occurrence group according to the presence of FGR. The ultrasound blood flow parameters ［systolic and diastolic velocity ratio (S/D), resistance index (RI), pulsatility index (PI)］, peripheral blood Gas6 level and clinical data of the two groups were compared, and the influencing factors of FGR in the third trimester of pregnancy were analyzed by Logistic regression analysis. The receiver operating characteristic (ROC) curve was plotted and the predictive value was assessed by the area under the ROC curve (AUC). 
Results Based on the follow-up until the end of pregnancy, 24 of 285 women in the third trimester developed FGR (8.42%), and the remaining 261 patients did not develop FGR. The proportion of cesarean section in the occurrence group was higher than that in the non-occurrence group (P＜0.05), and the newborn body weight in the occurrence group was lower than that in non-occurrence group (P＜0.05). The S/D (2.72±0.38), RI (0.85±0.17), and PI (1.08±0.32) of umbilical artery in the occurrence group were higher than those in the non-occurrence group ［(2.10±0.30), (0.59±0.13), (0.75±0.24)］ (P＜0.05). The S/D (3.41±0.48), RI (0.60±0.15), and PI (1.22±0.27) of uterine artery in the occurrence group were higher than those in the non-occurrence group ［(2.33±0.39), (0.37±0.08), (0.83±0.19)］ (P＜0.05). The level of Gas6 in peripheral blood of the occurrence group ［(12.67±2.41) g/L］ was higher than that in the non-occurrence group ［(9.25±1.78) g/L］ (P＜0.05). Uterine artery PI (OR=3.518, 95%CI: 1.547-8.004), fetal umbilical artery RI (OR=3.762, 95%CI: 1.654-8.558), fetal umbilical artery S/D (OR=2.907, 95%CI: 1.278-6.612) and peripheral blood Gas6 (OR=3.043, 95%CI: 1.338-6.923) were the influencing factors of FGR in the third trimester of pregnancy (P＜0.05).The AUC values of uterine artery PI, fetal umbilical artery RI, fetal umbilical artery S/D, peripheral blood Gas6 and their combination in predicting the incidence of FGR in pregnant women in the third trimester of pregnancy were 0.792, 0.803, 0.823, 0.815 and 0.899, respectively (P＜0.05), and the AUC value of the four indicators in combination was higher (P＜0.05). 
Conclusion The ultrasound blood flow parameters (uterine artery PI, fetal umbilical artery RI, fetal umbilical artery S/D) and peripheral blood Gas6 have important value in predicting FGR in pregnant women in the third trimester of pregnancy, and the combination of the four indicators has higher predictive value. 

Key words: fetal growth retardation, ultrasonography, prenatal, growth arrest specific protein 6