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Abstract PAS is associated with significant maternal and fetal morbidity and mortality. These risks can be reduced by antenatal diagnosis and multidisciplinary planning for delivery. US evaluation, with grayscale and CDI, is the recommended first-line modality for diagnosing PAS. To optimize the diagnosis, Rac et al. (2015) designed the PAI score for pregnancies in the third trimester based on US parameters in a high-risk population. They reported that the probability of histopathological invasion increases with increasing PAI score. However, they admitted the retrospective nature of their work. This study aimed to evaluate the diagnostic performance of the PAI in the prediction of PAS in correlation with histopathological findings. This was a prospective cohort study of 100 pregnant women recruited from the Obstetrics and Gynecology department, Mansoura University Hospitals between July 2017 to December 2018. Those women had a single fetus in the third trimester of pregnancy, with an anterior low-lying placenta or placenta previa and a previous delivery by at least 1 CS. The PAI score (a 9 point score) was calculated for every case and compared with histopathological findings. PAI includes the number of previous CS, grading of placental lacunae, smallest myometrial thickness, anterior low lying or placenta previa and bridging vessels. Histopathological confirmation of PAS was obtained in women who underwent a CS hysterectomy. Cases in which CS hysterectomy was not performed and those without histopathological confirmation of PAS on CS hysterectomy were considered the comparative group. We found that with a cut-off point > 5.37, the PAI has a sensitivity of 83.9%, a specificity of 76.3%, a PPV of 85.2%, and a NPV of 74.3% for a histopathologically proven PAS. The Accuracy was 81% with AUC 0.837. Women with histopathologically proven PAS (n=23) had significantly increased mean PAI score (7.72±1.51 vs. 5.27±2.01, P<0.001), number of previous CS (95.7% vs. 72.7%, P=0.02), higher lacunae grade (91.3% vs. 53.3%, P<0.001), reduced sagittal smallest myometrial thickness (1mm vs. 2mm, P=0.002), and more bridging vessels (95.7% vs. 72.7%, P=0.02) compared to non PAS patients (n=77). Significant differences between PAS and non PAS patient groups regarding intraoperative and postoperative data were found. Based on our study, the application of PAI is useful in clinical practice for predicting PAS in patients at risk. |