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Clinical features, diagnosis, and course of placenta previa

Charles J Lockwood, MD, MHCM
Karen Russo-Stieglitz, MD
Section Editors
Deborah Levine, MD
Susan M Ramin, MD
Deputy Editor
Vanessa A Barss, MD, FACOG


Placenta previa refers to the presence of placental tissue that extends over the internal cervical os. Sequelae include the potential for severe bleeding and preterm birth, as well as the need for cesarean delivery.

Placenta previa should be suspected in any woman beyond 20 weeks of gestation who presents with painless vaginal bleeding. For women who have not had a second trimester ultrasound examination, antepartum bleeding after 20 weeks of gestation should prompt sonographic determination of placental location before digital vaginal examination is performed because palpation of the placenta can cause severe hemorrhage.


In a systematic review including 58 observational studies of placenta previa, incidence ranged from 3.5 to 4.6 per 1000 births [1]. The incidence is severalfold higher early in gestation, but most of these cases resolve before delivery (see 'Ultrasound presentation and course' below).

Purported risk factors, some of which are interdependent, include [2-13]:

Previous placenta previa


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Literature review current through: May 2017. | This topic last updated: Nov 30, 2016.
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