Placenta Accreta Spectrum Diagnosis and Management

Diagnostic Criteria

The American College of Radiology suggests that placenta accreta spectrum (PAS) occurs when placental villi adhere directly to or invade the myometrium due to decidual deficiency, preventing normal placental separation in patients with a history of uterine surgery or placenta previa 1, 2.
The absence of a plane of separation is a hallmark finding of PAS, as normal placentas separate through the decidual separation zone, which is absent or deficient in PAS, and this is supported by the American College of Radiology 3, 2.
Minimal bleeding distinguishes PAS from other causes of retained placenta, as the placenta remains adherent and intact, preventing massive hemorrhage, according to the American College of Obstetricians and Gynecologists 4, 5.

Manual removal or gentle traction fails to deliver the placenta in PAS due to abnormal attachment to myometrial smooth muscle fibers, and the American College of Obstetricians and Gynecologists recommends avoiding forced removal 6, 4.
Pathology guidelines identify manual removal, retained placenta, and gross disruption of the maternal surface as clinical indicators warranting evaluation for PAS, as stated by the College of American Pathologists 6, 4.
The presence of placenta previa with prior cesarean delivery dramatically increases PAS risk, with an 11% risk with one prior cesarean and up to 67% with five or more, according to the American College of Obstetricians and Gynecologists 7, 8.

Attempting forced placental removal when PAS is present can cause catastrophic hemorrhage and should be avoided, and the placenta should be left in situ, as recommended by the Society for Maternal-Fetal Medicine 7, 9, 8.
If retained placenta with no plane of separation is encountered during vaginal delivery, immediate preparation for potential hysterectomy is warranted, with mobilization of a multidisciplinary team, according to the American College of Obstetricians and Gynecologists 7, 9.

The American College of Pathology recommends placental examination in cases of clinical suspicion of placenta accreta spectrum (PAS), particularly with placenta previa overlying a cesarean scar, retained placenta requiring manual removal, or maternal surface disruption 10

The presence of basal plate myometrial fibers (BPMF) in delivered placentas represents a distinct category from true PAS, and directed sampling at the junction between intact and disrupted areas increases detection of BPMF 11, 12
The detection of BPMF may indicate focal adherence and increased risk for PAS in subsequent pregnancies 12