MIAMI BEACH — Pelvic ultrasound is accurate for ruling out placenta accreta, and should be used as the primary screening tool in patients at high risk for this condition, Dr. Carri Warshak said at the annual meeting of the Society for Maternal-Fetal Medicine.
Magnetic resonance imaging also should be considered in the evaluation of all suspected cases, she added.
A historical cohort study of 433 patients with placenta previa who underwent ultrasound showed that this screening modality accurately predicted placenta accreta (which for the purposes of this study also included placenta increta and percreta) in 25 of the 32 women whose diagnosis was confirmed by pathologic examination, for a sensitivity of 0.78.
Ultrasound ruled out the condition in 397 of 401 patients, for a specificity of 0.99; MRI ruled out the condition in the remaining 4 patients, reported Dr. Warshak of the University of California, San Diego.
Of an additional 58 women who were referred for MRI based on equivocal ultrasound findings, 39 were shown on pathologic examination to have placenta accreta. MRI accurately predicted the condition in 35 of the 39 patients for a sensitivity of 0.90, and ruled out the condition in the remaining 19 patients for a specificity of 1.
Information for the study was obtained from a perinatal database for patients screened by ultrasound between January 2000 and June 2005 and for patients screened by MRI between January 1992 and June 2005. The findings are important because they confirm the accuracy of ultrasound and MRI for detecting a condition that requires accurate prenatal diagnosis for optimal management, she said.
Furthermore, the incidence of abnormal placentation has increased 10-fold over the past decade, largely due to the increased cesarean section rate. An estimated 9% of pregnancies are affected, she noted.
The findings confirm those from the three largest studies of ultrasound diagnosis for placenta accreta; pooled data from those studies and the current study show pelvic ultrasound is 81% sensitive and 98% specific for diagnosis, she said.
MRI has been less well studied, and results have been conflicting, but the findings of this study suggest it has an important role in optimizing diagnostic accuracy, particularly in patients with equivocal findings on ultrasound, she concluded.