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). In women with placenta previa, the placenta is situated either very near or 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. Less than 10% of women with a low lying placenta are diagnosed with placenta previa.

There are three classifications 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 0.5% to 0.8% of all pregnancies.

Signs and Symptoms of Placenta Previa

· 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.

Risk Factors for Placenta Previa

Cigarette smoking

First pregnancy after a cesarean birth

Prior placenta previa (risk of repeat is 4-8%)

Advanced maternal age

Women with frequent pregnancy (up to 5% risk)

Multiple pregnancy

Prior history of induced abortion

Diagnosis of Placenta Previa

An ultrasound is done to determine the location of the placenta. In rare instances, a vaginal exam may be done. 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.

Treatment of Placenta Previa

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 a woman is diagnosed with placenta previa but not actively bleeding, the physician may continue the pregnancy to allow the preterm fetus to mature. The pregnant woman may be placed on bed rest at home. She will be instructed to call the physician if any bleeding occurs. Additionally, she will be instructed to avoid stimulating the cervix; she must abstain from sex, vaginal manipulation, and douching. If a woman is bleeding, 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.

The prognosis for the term baby is good. The prognosis for the premature baby depends upon the weeks of gestation and condition at birth.