Placenta Accreta Spectrum

Placenta Accreta Spectrum

Alireza A. Shamshirsaz

Amy R. Mehollin-Ray

Karin A. Fox

Amir A. Shamshirsaz

Michael A. Belfort


Physical Examination

  • PAS should be considered in all pregnant women with a history of prior cesarean delivery and placenta previa.

  • Digital cervical examination should be avoided until placenta previa is ruled out in PAS cases.

  • Cautious sterile speculum vaginal examination should only be performed in a patient with PAS if there is important information that can be gained. The same precautions should be taken as with placenta previa patients.

  • Fetal evaluation is unaltered from that in normal pregnancy although oxytocin challenge test is usually contraindicated.

  • Definitive diagnosis is via imaging (see the section for Imaging and Other Diagnostics).

  • An accurate obstetrical and surgical history is essential because placenta previa significantly increases the risk of PAS in case of prior cesarean delivery or uterine surgeries.

Differential Diagnosis

  • Placenta previa

  • Uterine rupture/dehiscence

Nonoperative Management

  • Serial ultrasound monitoring of placental location before delivery as described in the section for imaging.

  • Vaginal bleeding should be monitored, and patient precaution should be given regarding pelvic rest.


  • Universal screening for placental location during the midtrimester anatomy scan.

  • First-trimester ultrasound markers: Several PAS ultrasound markers have been described in the first trimester. In a patient with a previous cesarean delivery, implantation of the gestational sac in the lower uterine segment is one of the most common markers for PAS in the first trimester. A cesarean scar pregnancy (CSP), defined as a gestational sac implanted in the lower uterine segment within or in close proximity to the cesarean scar, markedly increases the risk of PAS (27,28). CSP has been covered in Chapter 1.6. In the late first trimester, low implantation of the gestational sac is identified in ˜28% of patients with PAS (27). Other markers that have traditionally been described in second and third-trimester scans have also been identified in the late first trimester and are variably associated with PAS, as explained below (29).

  • Second- and third-trimester ultrasound markers (30):

    • Placental lacunae (Figure 4.9.4):

      • Irregular, hypo-, or anechoic spaces within the placenta showing vascular flow (seen on grayscale and color Doppler imaging). The following lacunae findings are associated with a high risk of PAS:

        • Multiple (often defined as >3)

        • Large size

        • Irregular borders

        • High velocity and/or turbulent flow within

      • Absence of lacunae in pregnancies with placenta previa and previous cesarean delivery is a reassuring sign with negative predictive values (NPV) ranging from 88% to 100% for PAS (31,32).

    • Abnormal uteroplacental interface:

      • Loss of the retroplacental hypoechoic zone between the placenta and myometrium, often noted between the uterus and posterior bladder wall, resulting in partial or complete interruption of the uterovesical interface (Figure 4.9.4)

      • Thinning of the retroplacental myometrium (thickness of <1 mm). This marker can be simulated by undue transducer pressure; therefore, during imaging of the placenta, transducer pressure on the abdomen should be minimized (33).

    • Abnormal uterine contour (placental bulge): Placental tissue distorting the outer uterine contour resulting in a bulge-like appearance (Figures 4.9.4 and 4.9.5A)

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Sep 9, 2022 | Posted by in OBSTETRICS | Comments Off on Placenta Accreta Spectrum
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