Utility of Ultrasound and MRI in Prenatal Diagnosis of Placenta Accreta: A Pilot Study

OBJECTIVE. The purpose of this study was to evaluate transabdominal pelvic ultrasound and MRI for the prenatal diagnosis of placenta accreta. MATERIALS AND METHODS. A historical cohort pilot study was performed at our institution to identify women at risk of placenta accreta who had undergone both prenatal ultrasound and MRI. Findings at ultrasound and MRI were compared with the final diagnosis, which was established with clinical findings at delivery and pathologic examination of specimens. Volume measurements were made of low-signal-intensity intraplacental bands on T2-weighted MR images. Risk factors for placental insufficiency were recorded. RESULTS. Thirteen patients at risk of placenta accreta underwent both sonography and MRI. Nine of these patients had abnormal placentation. With ultrasound, abnormal placentation was correctly identified in six of nine patients (67%) and the absence of accreta in two of four patients (50%). With MRI, abnormal placentation was correctly identified in seven of nine patients (78%) and the absence of accreta in three of four patients (75%). The volumes of low-signal-intensity bands were significantly different in the patients with abnormal placentation and those without placenta accreta (p = 0.047), and band volumes were significantly different among patients with accreta, increta, and percreta (p < 0.0005). CONCLUSION. The accuracy of MRI may improve if volumes of low-signal-intensity bands are calculated, MRI is performed before 30 weeks' gestation, and risk factors for placental insufficiency are recognized.