Description | Incidence of Placenta Previa | Signs and Symptoms | Risk Factors | Diagnosis | Treatment | Outcome

Description of Placenta Previa

The placenta and umbilical cord connect the mother and the developing baby. The placenta provides nutrients to the baby and eliminates waste products through a filtering system. Normally, the placenta is located near the top of the uterus (the fundus). Diagnosis of a low lying placenta during an ultrasound indicates that the placenta is located in the lower half of the uterus, In women with placenta previa, the placenta is situated either very near, partially or completely covering the opening of the cervix. The placenta placement causes a risk of hemorrhage (excessive bleeding) which can threaten the well being of the mother and the baby.

In 4-8% of women, the placenta is found to be in a low lying position in early pregnancy (and even as late as early in the third trimester). However, in most cases, the placenta moves up toward the top of the uterus as the pregnancy approaches term and the uterus expands in size. Less than 10% of women with a low lying placenta are diagnosed with placenta previa.

There are three types of placenta previa:

Marginal previa. The edge of the placenta is very near the opening of the cervix. When the cervix dilates during labor, the placenta may move upward or it may partially block the birth canal. Marginal previa presents a risk of hemorrhage during labor and delivery. While a vaginal delivery is possible in some circumstances, a cesarean is more likely.
Partial previa. The placenta partly covers the cervical opening. Normal labor and delivery would probably result in hemorrhage as the placenta is damaged by pressure from the baby. The phsycian will perform a cesarean.
Total previa. The placenta completely covers the cervical opening. The baby will need to be delivered by cesarean.

While vaginal bleeding is frightening, the first bleed with placenta previa is rarely fatal. If the placenta is maintaining the fetus, the baby’s greatest risk is from premature birth. The fetus is at increased risk for intrauterine growth retardation because the placenta may not provide optimal nutrition for the developing baby.
A woman with placenta previa should abstain from sexual intercourse or other vaginal manipulation. She should not use tampons or douche. Stimulation of the cervix can cause bleeding. Vaginal exams may also result in bleeding.

Incidence of Placenta Previa

Placenta previa is rare. It occurs in 1 of all 200-250 pregnancies. If the previa is diagnosed by ultrasound before 20 weeks, research shows it persists about two percent of the time. If this is accompanied by bleeding (called symptomatic placenta previa), or you were diagnosed with previa later in your pregnancy, there is an increased risk that the placenta will not move upward.

Signs and Symptoms of Placenta Previa

Sudden, painless bright red vaginal bleeding in the second or third trimester. The bleeding may be heavy or scant. Often, the bleeding will stop spontaneously, but it generally reoccurs. Obviously, any bleeding in the second or third trimester should be immediately reported to the practitioner. The first bleed occurs,on average, at 27-32 weeks' gestation. Contractions may or may not occur simultaneously with the bleeding.

Risk Factors for Placenta Previa

Although there are no specific causes of placenta previa, there are some factors that may increase your risks for the disorder:

• Cigarette smoking.
• First pregnancy after a cesarean birth.
• The risk increases to 1-4 % after one previous cesarean delivery and up to 10% after four or more cesarean deliveries.
• Prior placenta previa (risk of repeat is 4-8%)
  
• Advanced maternal age (women over 30 are 3 times more likely to have placenta previa then women under 20)
• Women with frequent pregnancy (up to 5% risk)
• Multiple pregnancy
• Prior history of induced abortion
• There is an increased risk of placenta previa among African Americans and Asians.
• Sever scarring of the uturus.
• Placenta accreta, an abnormally firm attachment of the placenta to the uterine wall.
• One study suggests a higher incidence of Placenta Previa in pregnancies of male fetuses.
  
  

Diagnosis of Placenta Previa

Low lying placentas are often diagnosed during routine ultrasounds done in early pregnancy. If you were found to have a low-lying placenta, your doctor may order another ultrasound around week 28 to determine the location of the placenta.

If you have not been diagnosed with a low lying placenta by ultrasound, you may be diagnosed after having unexplained, painless bleeding in your second or third trimesters. (If this is the case, a vaginal exam should be avoided until the placenta previa can be ruled out. If the physician performs a vaginal exam, the exam will be performed in an operating room which is readied for a cesarean section because of the risk of hemorrhage during the exam.)

Other reasons to suspect a previa would sometimes be premature contractions, abnormal lie (breech, transverse, etc.) of the baby, or the uterus measuring larger than it should according to dates.

Treatment of Placenta Previa

There is no way for you to control or promote the placenta to move upward. The management of placenta previa depends upon the type (marginal, partial or complete), the maturity of the fetus, and the presence of active bleeding.

If you are diagnosed with placenta previa but not actively bleeding, the physician may:

• Continue the pregnancy to allow the preterm fetus to mature.
• Increase your iron intake to compensate for additional blood loss which may occur.
• Instruct you to call him if any bleeding occurs.
• Instructed you to avoid stimulating the cervix; abstain from sex, vaginal manipulation, and douching.
• You may be forbidden to any lifting, stenuous work, or aerobic exercise.
• You may be placed on bed rest at home.

If you are bleeding, you will be hospitalized, the baby will be stabilized, and the physician will try to assess the maturity of the fetus and the degree of blood loss. An amniocentesis will probably be done to evaluate the maturity of the baby’s lungs in case an emergency cesarean is required. Blood tests will be run on the mother (Complete blood count, Typing and crossmatch) to evaluate blood loss and prepare for transfusions if necessary. If the infant’s lungs are not mature, the phsycian may try to stabilize the mother and give her a steroid injection to hasten fetal lung maturation. The mother may be treated with intravenous fluids to maintain fluid volume, blood or plasma transfusions to replace loss. The mother will receive oxygen since blood loss reduces blood oxygen levels and places the fetus at risk for insufficient oxygenation. Fetal monitoring will be used to gauge fetal well being. If hemorrhage is severe, the baby will be delivered by cesarean section even if the lungs are immature. The hemorrhaging placenta cannot nourish the baby and the severe blood loss places the mother at risk. If an fetus’ lungs are mature, a woman with partial or complete placenta previa will require a cesarean. In some instances, a woman with a marginal previa may be able to deliver vaginally. Whenever possible, the woman should deliver at a hospital facility that has intensive care services for mother and newborn.

Prognosis:

True placenta previa at term is very serious. The prognosis for the term baby is good. The prognosis for the premature baby depends upon the weeks of gestation and condition at birth. Complications for the baby include:

• Problems for the baby, secondary to acute blood loss.
• Intrauterine growth retardation due to poor placental perfusion.
• Increased incidence of congenital anomalies.

There is a maternal morbidity rate of .03%. Risks for the mother include:

• Life-threatening hemorrhage during which a blood transfusion may need to be performed.
• Cesarean delivery.
• Increased risk of postpartum hemorrhage
• Increased risk placenta accreta (Placenta accreta is where the placenta attaches directly to the uterine muscle.)

The great majority of deaths are related to uterine bleeding and the complication of disseminated intravascular coagulopathy.

Cited Sources:

1. ** Parents Place: "What are the chances the placenta will move up?" by Peg Plumbo, CNM.
2. **** eMedicine: Placenta Previa. by Young Yoon, MD and Patrick Ko, MD.
3. *** "Managing Placentia Previa". by Cecelia A. Cancellaro.
4. **** "MediFocus MedCenter © Placenta Previa".
5. ***** "Placenta Previa" from About.com.
6. *** Placenta Previa Ultrasound Images
7. * "Placenta Previa More Common with Birth of Male Babies" from OBGyn.net.
8. ***** "Placenta Previa : Basic Information" from MoonDragon. (Don't let the name fool you, good info and pictures.)
   

Support:

• "Let's Talk Previa" Delphi Support Forum
• "Complications in Pregnancy EZboard : Placenta Previa Support"
  
  

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