Abstract: Objective To study the value of ultrasound evaluation of blood flow parameters (S wave, D wave, A wave) combined with placenta protein-13 detection in the prediction of late-onset intrauterine growth restriction (FGR). 
Methods A total of 130 pregnant women who gave birth in the Department of Obstetrics and Gynecology of our hospital from December 2022 to December 2023 were selected, including 42 patients with late-onset FGR (observation group) and 88 patients with normal FGR (control group). According to the blood flow characteristics of umbilical artery and uterine artery, the patients with late-onset FGR were divided into group Ⅰ, group Ⅱ, group Ⅲ and group Ⅳ. The blood flow velocity (S wave, D wave, A wave) and serum placenta protein-13 levels of intravenous catheter were compared between the observation group and the control group, and the differences of various indexes in patients with late-onset FGR in different subgroups were analyzed. The predictive value of intravenous catheter blood flow velocity (S wave, D wave, A wave) and serum placenta protein-1 for late-onset FGR was analyzed by receiver operating characteristic (ROC) curve. 
Results The S wave ［(55.84±8.46） cm/s vs. （60.67±7.78） cm/s］, D wave ［(42.89±6.64） cm/s vs. （48.38±7.47） cm/s］, A wave ［(23.35±4.58） cm/s vs. （31.68±4.45） cm/s］ and serum placental protein-13 ［(0.98±0.15） cm/s vs. （1.15±0.18） cm/s］ in the observation group were lower than those in the control group (P＜0.05). There were significant differences in blood flow velocity (S wave, D wave, A wave) and serum placental protein-13 levels in different subtypes of pregnant women, and the levels of S wave, D wave, A wave and serum placental protein-13 showed an increasing trend with the increase of grade (P＜0.05). Logistic regression analysis showed that intravenous catheter blood flow velocity (S wave, D wave, A wave) and serum placenta protein-13 were the influential factors of FGR in late pregnancy (P＜0.05). ROC curve analysis showed that the area under the ROC curve (AUC) of S wave, D wave, A wave and serum placenta protein-13 for predicting FGR was 0.766 (95%CI: 0.672-0.861), 0.765 (95%CI: 0.663-0.862), 0.751 (95%CI: 0.653-0.856) and 0.816 (95%CI: 0.717-0.916), respectively, the AUC of combined prediction for FGR was 0.875 (95%CI: 0.793-0.952), and the AUC of combined prediction for FGR was higher than that of single prediction (P＜0.05). 
Conclusion The intravenous catheter blood flow velocity (S wave, D wave, A wave) and placenta protein-13 are closely related to the occurrence and development of FGR, and the combined detection can improve the prediction efficiency of FGR. 

Key words: fetal growth retardation, ultrasound, placentin-13