DIAGNOSTIC ACCURACY OF PLACENTA INVASION IN LOWER UTERINE SEGMENT MEASURED BY ULTRASOUND IN PREDICTION OF PLACENTA ACCRETA SPECTRUM AND ITS CORRELATION WITH GROSS PATHOLOGY POSTOPERATIVE

Abstract

Background: Placenta Accreta Spectrum (PAS) is a leading cause of severe obstetric hemorrhage and maternal morbidity, with increasing incidence due to rising cesarean section rates. Accurate prenatal diagnosis is essential for optimizing surgical planning and reducing complications. Ultrasound is the primary imaging modality; however, its diagnostic performance in the lower uterine segment (LUS) requires further validation against a pathological reference standard. Objective: To evaluate the diagnostic accuracy of gray-scale and Doppler ultrasound in detecting Placenta Accreta Spectrum through assessment of the lower uterine segment, using histopathological findings as the reference standard in a high-risk cohort. Methods: This cross-sectional analytical study included 40 pregnant women with suspected PAS at a tertiary care hospital in Karachi, Pakistan. All participants underwent standardized gray-scale and Doppler ultrasound evaluation of the LUS prior to cesarean delivery. Sonographic findings were compared with postoperative histopathological diagnosis. Sensitivity and positive predictive value (PPV) were calculated with 95% confidence intervals. Due to the very small number of histopathology-negative cases, specificity and negative predictive value (NPV) could not be reliably estimated. Results: PAS was confirmed in 38 of 40 cases (94.9%). Ultrasound demonstrated a sensitivity of 89.2% (95% CI: 75.3%–95.7%) and a PPV of 94.3% (95% CI: 81.4%–98.4%). Loss of the retroplacental clear zone (87.2%) and placental lacunae (82.1%) were the most frequently identified ultrasound features. Obstetric hysterectomy was performed in 94.9% of cases, with a mean estimated blood loss of 2354 ± 530 ml. No maternal mortality was recorded. Diagnostic performance estimates are influenced by the high prevalence of PAS in this selected high-risk cohort. Conclusion: Ultrasound demonstrates high sensitivity and strong positive predictive value for detecting PAS in high-risk populations when assessing the lower uterine segment. However, diagnostic performance is affected by spectrum bias, limiting generalizability. Larger multicenter studies with more balanced populations are required to validate these findings