Placenta previa

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[edit] Discussion of Placenta previa

  • Placenta previa is a condition in which the placental tissue lies abnormally close to or over the internal cervical os.
  • Subtypes of placenta previa
    • Complete: placenta covers the entire internal cervical os
    • Partial: placenta partially covers the internal cervical os
    • Marginal: Placental tissue abuts but does not cover the internal cervical os
    • Low lying: Edge of the placenta lies abnormally close to but does not abut the internal cervical os.


  • Risk factors for placenta previa include prior placenta previa, prior cesarean delivery, increased maternal age, large placentae (eg, multiple gestations or erythroblastosis), and a maternal history of smoking.


  • As the lower uterine segment thins in late pregnancy, the margins of the abnormally implanted placenta are altered.
  • Various degrees of placental detachment may develop, with ensuing maternal hemorrhage from the intervillous space.
  • During labor, significant fetal hemorrhage also can occur as a result of disrupted villous placental vessels.

[edit] Imaging Findings for Placenta previa

  • US: If the internal cervical os can be visualized and if no placental tissue overlies it, placenta previa is excluded.
  • MRI: Sagittal images best demonstrate the placental position in relation to the internal cervical os.


[edit] Images

Patient #1: MRI demonstrates a complete placenta previa

[edit] See also

[edit] External Links

[edit] References for Placenta previa