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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 connects mother and fetus, transferring oxygen and nutrients from the mother to the fetus. The placenta is disk-shaped and at full term measures about 7 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 placenta previa?
Bleeding is the primary symptom of placenta previa and occurs in the majority (70%-80%) of women with this condition.
What are the types of placenta previa?The types of placenta previa include the following:
The term low-lying placenta or low placenta has been used to refer both to placenta previa and marginal placenta previa. Sometimes, the terms anterior placenta previa and posterior placenta previa are used to further define the exact position of the placenta within the uterus, as defined by ultrasound examinations. IMAGESPlacenta Previa See pictures of a growing fetus through the 3 stages of pregnancy See ImagesWhat 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. What uterine factors contribute to the development of placenta previa?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. What placental factors contribute to the development of placenta previa?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:
How many pregnant women have placenta previa? Who is at risk?Placenta previa is found in approximately 4 out of every 1000 pregnancies beyond the 20th week of gestation. Risk factors include the following:
How is placenta previa diagnosed?
An ultrasound examination is used to establish the diagnosis of placenta previa. Either a transabdominal (using a probe on the abdominal wall) or transvaginal (with a probe inserted inside the vagina but away from the cervical opening) ultrasound evaluation may be performed, depending upon the location of the placenta. Sometimes both types of ultrasound examination are necessary. It is important that the ultrasound examination be performed before a physical examination of the pelvis in women with suspected placenta previa, since the pelvic physical examination may lead to further bleeding. SLIDESHOWStages of Pregnancy: Week by Week See SlideshowWhat is the treatment and management for placenta previa?
Treatment of placenta previa depends upon the:
Cesarean delivery (C-section) is required for complete placenta previa and may be necessary for other types of placenta previa. A Cesarean delivery is usually planned for women with placenta previa as soon as the baby can be safely delivered (typically after 36 weeks' gestation), although an emergency Cesarean delivery at any earlier gestational age may be necessary for heavy bleeding that cannot be stopped after treatment in the hospital (see below). Women who are actively bleeding or who have bleeding that cannot be stopped will be admitted to the hospital for further care. If there has been little or no bleeding or the bleeding has stopped, bed rest at home may be prescribed. Home care is not always appropriate, and women who remain at home must be able to access medical care immediately should bleeding resume. Women with placenta previa in the 3rd trimester of pregnancy are advised to avoid sexual intercourse and exercise and to reduce their activity level. Women with placenta previa who experience heavy bleeding may require blood transfusions and intravenous fluids. In some cases, tocolytic drugs (medications that slow down or inhibit labor), such as magnesium sulfate or terbutaline (Brethine) are necessary. Corticosteroids may be given to enhance lung development in the fetus prior to Cesarean delivery. Subscribe to MedicineNet's Pregnancy & Newborns NewsletterBy clicking "Submit," I agree to the MedicineNet Terms and Conditions and Privacy Policy. I also agree to receive emails from MedicineNet and I understand that I may opt out of MedicineNet subscriptions at any time. What are complications of placenta previa? Is it harmful to the fetus and baby?
What is the prognosis for a woman with placenta previa during pregnancy?
The majority of women with placenta previa in developed countries will deliver healthy babies, and the maternal mortality (death) rate is less than 1%. In developing countries where medical resources may be lacking, the risks for mother and fetus may be higher. How can you prevent placenta previa during pregnancy?Placenta previa cannot typically be prevented. In some cases, risk factors for the development of placenta previa can be eliminated (such as smoking cessation). FromMedically Reviewed on 4/1/2022 References Bakker, R, MD, et al. Placenta Previa. Medscape. Updated: Jan 08, 2017. Why does placenta previa happen?KEY POINTS. Placenta previa happens when the placenta lies low in the uterus and covers all or part of the opening to the vagina. If you develop the condition early in your pregnancy, it usually isn't a problem since the placenta grows upward with the uterus during pregnancy.
How can you prevent placenta previa?How Can You Prevent Placenta Previa? Placenta previa usually cannot be prevented. In some cases, risk factors can be eliminated (such as smoking cessation). Bleeding from placenta previa can be reduced in many cases by bed rest, limitation of activity, and/or avoiding sexual intercourse.
What are the risk factors of placenta previa?Risk factors for placenta previa include the following:. Multiparity.. Prior cesarean delivery.. Uterine abnormalities that inhibit normal implantation (eg, fibroids, prior curettage). Prior uterine surgery (eg, myomectomy) or procedure (eg, multiple dilation and curettage [D and C] procedures). Smoking.. Multifetal pregnancy.. Can a baby survive placenta previa?Placenta previa can have serious adverse consequences for both mother and baby, including an increased risk of maternal and neonatal mortality[1–3], fetal growth restriction and preterm delivery[4], antenatal and intrapartum hemorrhage[5–7], and women may require a blood transfusion[8] or even an emergency hysterectomy ...
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