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Placenta previa is a complication of pregnancy in which the placenta grows in the lowest part of the womb (uterus) and covers all or part of the opening to the cervix.
The placenta is the organ that nourishes the developing baby in the womb.
During pregnancy, the placenta moves as the uterus stretches and grows. In early pregnancy, a low-lying placenta is very common. But as the pregnancy progresses, the growing uterus should "pull" the placenta toward the top of the womb. By the third trimester, the placenta should be near the top of the uterus, leaving the opening of the cervix clear for the delivery.
Sometimes, though, the placenta remains in the lower portion of the uterus, partly or completely covering this opening. This is called a previa.
There are different forms of placenta previa:
Placenta previa occurs in 1 out of 200 pregnancies. It is more common in women who have:
Women who smoke or have their children at an older age may also have an increased risk. Possible causes of placenta previa include:
Francois KE, Foley MR. Antepartum and postpartum hemorrhage. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics - Normal and Problem Pregnancies. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2007:chap 18.
Houry DE, Abbott JT. Acute complications of pregnancy. In: Marx J, ed. Rosen’s Emergency Medicine: Concepts and Clinical Practice. 6th ed. St Philadelphia, Pa: Mosby Elsevier; 2006:chap 177.
Cunnigham FG, Leveno KL, Bloom SL, et al . Obstetrical hemorrhage. In: Cunnigham FG, Leveno KL, Bloom SL, et al, eds. Williams Obstetrics. 22nd ed. New York, NY; McGraw-Hill; 2005:chap 35.
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