Abstract： Objective:To determine the clinical value of prenatal ultrasound in diagnosis of placenta previa and placenta accreta.Methods:The clinical data of 72 pregnant women with confirmed placenta previa in our hospital between January 2017 and December 2018 were collected. All pregnant women underwent prenatal ultrasound examination, including two-dimensional ultrasound and color Doppler ultrasound, and cesarean section. According to presence of placenta accreta, the subjects were divided into accreta group ( n=29) and non-accreta group ( n=43) . The association between placenta accreta and clinical data such as patient age and gestational history was analyzed. The differences in placental vascularization index (VI) , flow index (FI) and vascularization-flow index (VFI) were compared between the two groups. The diagnostic value of prenatal ultrasound for placenta previa and placenta accreta was determined. Results:The proportions of pregnant women with age ≥35 years old, cesarean section history, > two abortions, ≥three gestations were higher in the accreta group than those in non-accreta group (all P<0.05) . Of the accreta group, ultrasound identified 20 women (68.97%) with partial or complete vanishment of posterior placenta space, 11 (37.93%) with thin myometrium at placenta attachment or unclear placenta-myometrium boundary, 23 (79.31%) with placental lacuna sign, and 5 (17.24%) with abnormal thickening of placenta. The values of VI, FI and VFI in the accreta group were higher than those in the non-accreta group (all P<0.05) . The sensitivity and specificity for diagnosing placent accreta 93.10% and 90.70% by VFI with a cut-off value of 7.92, 86.21% and 79.07% by VI with a cut-off value of 18.05, and 82.76% and 58.14% by FI with a cut-off value of 33.61, respectively. Conclusion:In placenta previa complicated with placenta accreta, increased blood flow in placenta and bladder wall gives rise to relatively high placental vascularization. Three-dimensional power Doppler imaging may quantitatively measure the degree of placental vascularization and thereby offer a reliable basis for evaluation of prenatal placental accreta.