Background: Accurate antenatal diagnosis of an abnormally invasive placenta (AIP), allowing multidisciplinary management at the time of delivery, has been shown to improve maternal and fetal outcomes. Placenta previa and previous cesarean section are the two most important known risk factors for AIP. Objective: Comparison between the role of transabdominal ultrasound  (TAS) versus transvaginal ultrasound (TVS) in  evaluation of placental invasion in cases of placenta previa anterior wall with previous uterine scar applying the unified ultrasonography descriptors suggested by the European working group on abnormally invasive placenta "EW-AIP". Patients and Methods: Fifty pregnant women with persistent placenta previa (after 28 weeks' gestation) were prospectively enrolled into this study. Both transabdominal and transvaginal ultrasound were performed by two different operators who were blinded to the results of each other. The placenta was studied as regarding the exact localization and the unified descriptors were applied and evaluated by TAS and TVS. The ultrasound findings were analyzed with reference to the final diagnosis made during cesarean delivery and histopathological examination. Results: Abnormally invasive placenta and its variants were found in 43 patients at the time of cesarean delivery, and were later confirmed by histopathological evaluation. As regards Grey-scale criteria; the accuracy of detection of the loss of the retro placental clear zone was 76% by TVS and 54% by TAS, while that of the abnormal placental lacunae was 92 % by TVS and 88% by TAS. Myometrial Thinning detection accuracy was 66% by TVS and 72% by TAS, and Doppler assessment showed that the accuracy of detection of the uterovesical hyper vascularity was 84% by TVS and 88% by TAS. The detection of bridging vessels was 76% by TVS and 75% by TAS. The overall accuracy of detection of TAS was 91%, whereas that of TVS was about 97.1%. Conclusion: Both transabdominal and trasnvaginal ultrasound were complementary to each other with an upper hand to transvaginal ultrasound, with the safety of TVS being confirmed. The unified descriptors were found to be reliable in accurate diagnosis.