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Placenta Previa

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Placenta previa definition and facts

  • Placenta previa is the attachment of the placenta to the wall of the uterus in a location that completely or partially covers the uterine outlet (opening of the cervix).
  • Bleeding after the 20th week of gestation is the main symptom of placenta previa.
  • An ultrasound examination is used to establish the diagnosis of placenta previa.
  • Treatment of placenta previa involves bed rest and limitation of activity. Tocolytic medications, intravenous fluids, and blood transfusions may be required depending upon the severity of the condition.
  • A Cesarean delivery is required for complete placenta previa.
  • Other complications of pregnancy can be associated with placenta previa, but the majority of women deliver healthy babies.

What is placenta previa?

Placenta previa is the most common cause of painless bleeding in the later stages of pregnancy (after the 20th week). The placenta is a temporary organ that joins the mother and fetus and transfers oxygen and nutrients from the mother to the fetus. The placenta is disk-shaped and at full term measures about seven inches in diameter. The placenta attaches to the wall of the uterus (womb). Placenta previa is a complication that results from the placenta implanting either near to, or overlying, the outlet of the uterus (the opening of the uterus, the cervix).

Because the placenta is rich in blood vessels, if it is implanted near the outlet of the uterus, bleeding can occur when the cervix dilates or stretches.

What are the signs and symptoms of placenta previa?

Bleeding is the primary symptom of placenta previa and occurs in the majority (70%-80%) of women with this condition.

  • Vaginal bleeding after the 20th week of gestation is characteristic of placenta previa.
  • Usually the bleeding is painless, but it can be associated with uterine contractions and abdominal pain.
  • Bleeding may range in severity from light to severe.

What causes placenta previa?

The placenta may be located in the lower part of the uterus either covering or adjacent to the cervical outlet for a number of reasons. The placenta normally migrates away from the cervical opening as the pregnancy progresses, so women in the earlier stages of pregnancy are more likely to have placenta previa than are women at term. Although up to 6% of women between 10 and 20 weeks' gestation will have some evidence of placenta previa on ultrasound examination, 90% of these cases resolve on their own as the pregnancy progresses.

Placenta previa that persists beyond the 20th week of gestation can be due to abnormalities of the uterus that promote attachment of the placenta in the lower regions of the uterus or to factors that require an increased size of the placenta.

Uterine factors

Uterine factors that can predispose to placenta previa include scarring of the upper lining tissues of the uterus. This can occur because of prior Cesarean deliveries, prior instrumentation (such as D&C procedures for miscarriages or induced abortions) of the uterine cavity, or any type of surgery involving the uterus.

Placental factors

When the placenta must grow larger to compensate for decreased function (lowered ability to deliver oxygen and/or nutrients), there is an increased chance of developing placenta previa since the surface area of the placenta will be larger. Examples of situations in which there is need for greater placenta function, and a resultant increase in risk for placenta previa include multiple gestation, cigarette smoking in the mother, and living at high altitude.

Medically Reviewed by a Doctor on 10/4/2017

Source: MedicineNet.com
https://www.medicinenet.com/pregnancy_placenta_previa/article.htm

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