DIAGNOSTIC ACCURACY OF ULTRASOUND IN DETECTING PLACENTA ACCRETA KEEPING MRI AS GOLD STANDARD

Abstract

Background: The incidence of Placenta Accreta Spectrum (PAS) disorders has risen precipitously, paralleling global increases in cesarean delivery. Prenatal diagnosis is paramount for mitigating severe maternal morbidity, yet the diagnostic performance of first-line ultrasonography (USG) requires rigorous validation against magnetic resonance imaging (MRI) in clinical practice.

Objective: To determine the diagnostic accuracy of grayscale and Doppler ultrasound in detecting PAS disorders using 1.5T MRI as the gold standard.

Methods: This prospective cross-sectional study was conducted at a tertiary care hospital. We enrolled 138 pregnant women with anterior placenta previa and clinical suspicion of PAS. All participants underwent standardized transabdominal ultrasound followed by pelvic 1.5T MRI. Diagnostic accuracy measures including sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated against the MRI diagnosis.

Results: MRI confirmed PAS in 60 of 138 patients (43.5%). Ultrasound demonstrated a sensitivity of 66.7% (40/60 true positives) and a specificity of 35.9% (28/78 true negatives). However, ultrasound produced a high false-positive rate, leading to a low positive predictive value of 44.4% (40/90). It also missed 20 cases of PAS (false negatives), resulting in a negative predictive value of 58.3%. The overall diagnostic accuracy of ultrasound was 49.3%.

Conclusion: While ultrasound serves as a necessary screening tool, its moderate sensitivity and notably poor specificity result in a significant number of both false-positive and false-negative diagnoses. These limitations underscore the critical role of MRI as an essential complementary modality to confirm USG findings, prevent unnecessary interventions, and guide definitive surgical planning for true positive cases. A combined imaging approach is vital for optimizing patient outcomes.