Extension of placental tissue beyond endometrial lining

Described as morbidly adherent placenta (MAP), placental adhesive disorder, and abnormally invasive placenta

Pathology subtypes of placenta accreta, increta, and percreta based on depth of myometrial invasion

Be familiar with normal appearance of placenta and placental/myometrial interface on US

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  Normal pregnant uterus has inverted pear shape with smooth contour, no focal bulging

  
  
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  Normal placenta has uniform texture, intermediate echogenicity

  
  
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  Retroplacental hypoechoic zone or “clear zone” should be present over entire placental surface

  
  
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  Beware of excess transducer pressure and reverberation in near field mimicking loss of clear zone

Large, irregular, tornado-shaped placental vessels with turbulent flow are most sensitive US indicator of MAP

Multiple findings increase specificity

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  Look for loss of retroplacental “clear zone”

  
  
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  Look for uterine “bulge” (i.e., disruption of smoothly contoured, inverted pear shape)

  
  
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  Look for interruption of bladder wall/uterine interface

  
  
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  Look for “bridging vessels” extending beyond myometrium

  
  
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  Beware bladder varices as pitfall: Vessels in bladder mucosa not coming from placenta

Have high index of suspicion for MAP in setting of placenta previa with prior cesarean section

Use highest resolution transducer to “walk the scar” and assess uterine wall

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  Use high-MHz curved/linear transducer abdominally; use vaginal ultrasound for anterior placenta/previa

  
  
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  Keep bladder partly full during evaluation of uterine interface