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Placenta Previa

Placenta Previa Overview

Placenta previa is a complication of pregnancy in which the placenta (the organ that joins the mother and fetus and transfers oxygen and nutrients to the fetus) is implanted either near to or overlying the outlet of the uterus (womb). Placenta previa is found in approximately four out of every 1000 pregnancies beyond the 20th week of gestation. The main symptom of placenta previa is bleeding.

Several terms have been used to characterize placenta previa. The types of placenta previa include:

  • Complete placenta previa refers to the situation in which the placenta completely covers the opening from the womb to the cervix.

  • Partial placenta previa refers to the placenta that partially covers the cervical opening (since the cervical opening is not dilated until time for delivery approaches, this type of placenta previa occurs after the cervix has begin to dilate).

  • Marginal placenta previa refers to a placenta that is located adjacent to, but not covering, the cervical opening.

  • The term low-lying placenta or low placenta has been used to refer both to placenta previa and marginal placenta previa.

  • The terms anterior placenta previa and posterior placenta previa are sometimes used after ultrasound examination to further define the exact position of the placenta within the uterine cavity.

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