Diagnostic accuracy of ultrasound and MRI in the prenatal diagnosis of placenta accreta.

OBJECTIVE: To analyze the value of ultrasound followed by magnetic resonance imaging (MRI) in doubtful cases for antenatal detection of placenta accreta.

DESIGN: A prospective observational study.

SETTING: Hospital in the southern region, Saudi Arabia.

SAMPLE: Patients with a low-lying placenta or placenta previa.

METHODS: The placentas of all included cases were scanned in a systematic fashion using both gray-scale and color Doppler (transabdominal and transvaginal).

MAIN OUTCOME MEASURES: Explicit ultrasound criteria for placenta accreta were carefully applied, and any case with two or more criteria was labeled as highly suspicious. If only one criterion was detected, then the case was labeled as suspicious and MRI was applied.

RESULTS: Five hundred and seventy seven women had a diagnosis of low-lying placenta or placenta previa. Of these, 42 had placenta accreta confirmed after delivery by pathological examination, and 39 of these were diagnosed prenatally. Ultrasound accurately predicted placenta accreta in 33 of 39 of women and correctly ruled out placenta accreta in 512 of 514 without placenta accreta (sensitivity 95.1% and specificity 95.5%). Twenty (20) women underwent MRI because of suspicion of placenta accreta by ultrasonography. MRI accurately predicted placenta accreta in six of 20 cases and correctly ruled out placenta accreta in 10 of 20 cases (sensitivity 85.7% and specificity 76.9%).

CONCLUSION: Placenta accreta can be successfully detected prenatally using ultrasound. MRI can provide additional information in doubtful cases.