Objective: The purpose of this study was to determine whether ultrasonography can detect placenta accreta reliably in at-risk patients.
Study design: All patients with a previous cesarean delivery and an anterior placenta or placenta previa were evaluated prospectively at each visit for sonographic signs of placenta accreta (interruption of the posterior bladder wall-uterine interface, absence of the retroplacental clear zone, and placental lacunae).
Results: This evaluation involved 2002 patients over a 12-year period. Of the 14 patients with a confirmed diagnosis of placenta accreta who had ultrasound examinations between 15 and 20 weeks of gestation, the diagnosis was suspected strongly in 86% of the patients (12/14 patients). There were 18 false-positive cases (54.5%; 18/33 patients), most of which were due to a lack of visualization of the echolucent area between the placenta and the myometrium (obliteration of the 'clear space') during the third trimester. The presence of multiple linear irregular vascular spaces within the placenta (placental lacunae) was the diagnostic sign with the highest positive predictive value for placenta accreta.
Conclusion: Placenta accreta can be detected as early as 15 to 20 weeks of gestation in most at-risk patients by visualization of irregular vascular spaces within the placenta (placental lacunae). Obliteration of the retroplacental 'clear space' is not a reliable diagnostic sign for placenta accreta.