Background: The aim of our study was to evaluate the accuracy of Three Dimensional Tomographic Ultrasound Imaging (3D-TUI) and 3D power Doppler using Alalfy simple criteria in the diagnosis of placenta previa and PAS (Placenta accrete spectrum) with differentiation of placenta previa (non-adherent placenta) from PAS disorders and determination of its subtypes (Accreta, increta, and percreta). Methods: A prospective observational study that included 90 pregnant women was made at Algezeera Hospital, Egypt. A systematic combined approach using Alalfy simple criteria; with applying the ultrasound criteria suggestive of PAS in the 3D-TUI, and 3D power Doppler ultrasound volume was performed to scan the placenta previa and to assess if it is non-adherent or PAS and to determine its subtype (accreta, increta or percreta). Results: The study shows a high agreement between the 3D-TUI with 3D power Doppler US using Alalfy simple criteria and the operative findings in the diagnosis and differentiation of placenta previa (non-adherent) from PAS (adherent) and its subtypes. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of the 3D-TUI cuts in diagnosing adherent from non-adherent were 100%, 100%, 100%, 100% and 100%, respectively. 3D TUI-cuts has a diagnostic accuracy of 98.8 percent when compared to operative findings in accurately determining the exact subtype of placenta accreta spectrum. Conclusion: The systematic combined approach using Alalfy Simple Criteria for assessment of placenta previa and PAS that entails applying the ultrasound criteria suggestive of PAS in the 3D-TUI—3D power Doppler volume has a high degree of accuracy in the diagnosis of PAS from non-adherent placenta and in accurately diagnosing the subtype of PAS (accreta, increta or percreta). 3D-TUI-cuts facilitates the evaluation of the myometrial thickness and the depth of placental invasion with much better differentiation between different subtypes of PAS with better identification of focal from diffuse invasion with the ability of 3D power Doppler to delineate the vessels invading a part of the myometrium or the whole myometrium, and bridging vessels and high vascularity.