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Causes
By Mayo Clinic staff
The placenta grows wherever the embryo implants itself in the uterus. If the embryo implants itself in the lower portion of the uterus, the placenta might grow over the cervix — causing placenta previa.
Most cases of placenta previa are diagnosed at the time of a second trimester ultrasound examination. If the placenta is just barely reaching the cervix, the situation will resolve itself because expansion of the uterus pulls the area of placental attachment higher up in the uterus, away from the cervical opening. If the placenta is found to be all the way across the cervix, however, it is unlikely to resolve with time.
Persistent types of placenta previa have been associated with:
- Scars in the lining of the uterus
- A large placenta, such as with a multiple pregnancy
- An abnormally shaped uterus
- Kay HH. Placenta previa and abruption. In: Gibbs RS, et al. Danforth's Obstetrics and Gynecology. 10th ed. Philadelphia, Pa.: Wolters Kluwer Health Lippincott Williams & Wilkins; 2008. http://www.danforthsobgyn.com. Accessed March 29, 2011.
- Bleeding during pregnancy. American Congress of Obstetricians and Gynecologists. http://www.acog.org/publications/patient_education/bp038.cfm. Accessed March 29, 2011.
- Houry DE, et al. Vaginal bleeding in later pregnancy. In: Marx JA, et al. Rosen's Emergency Medicine: Concepts and Clinical Practice. 7th ed. Philadelphia, Pa.: Mosby Elsevier; 2010. http://www.mdconsult.com/books/about.do?about=true&eid=4-u1.0-B978-0-323-05472-0..X0001-1--TOP&isbn=978-0-323-05472-0&uniqId=230100505-57. Accessed March 30, 2011.
- Williams DE, et al. Placenta previa. In: Rakel RE. Textbook of Family Medicine. 7th ed. Philadelphia, Pa.: Saunders Elsevier; 2007. http://www.mdconsult.com/das/book/body/191205553-4/0/1481/0.html#. Accessed March 30, 2011.
- Ramin KD, et al. Placenta previa. In: Bope ET, et al. Conn's Current Therapy. Philadelphia, Pa.: Saunders Elsevier; 2011. http://www.mdconsult.com/books/about.do?eid=4-u1.0-B978-1-4377-0986-5..C2009-0-38984-9--TOP&isbn=978-1-4377-0986-5&about=true&uniqId=236797353-5. Accessed March 30, 2011.
- Lockwood CJ, et al. Clinical manifestations and diagnosis of placenta previa. http://uptodate.com/home/index.html. Accessed March 30, 2011.
- Lockwood CJ, et al. Management of placenta previa. http://uptodate.com/home/index.html. Accessed March 30, 2011.
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