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When the placenta implants over or near the inner opening of the cervix, the condition is called placenta previa. The cervix is the opening of the uterus. As the cervix dilates during labor, the abnormal location of the placenta may cause heavy vaginal bleeding and keep the baby from traveling through the birth canal.

What is going on in the body?

Placenta previa occurs in 1 out of 200 births. In about 10% to 20% of these cases, the placenta covers the entire cervix.

This is called a complete placenta previa. Otherwise, if only part of the cervix is covered, this is called a partial placenta previa.

• as the lower part of the uterus starts to widen and thin out as the uterus grows in the later part of pregnancy
• as the cervix opens during labor, which tears blood vessels in the placenta
• with trauma to the placenta, as with the pressure of the penis during intercourse

The extent of the bleeding depends upon how much of the placenta covers the cervix and how many blood vessels are torn.

What are the signs and symptoms of the condition?

• sudden, painless, bright red vaginal bleeding, usually in the later half of pregnancy
• painless vaginal bleeding after sexual intercourse
• uterine cramping with the bleeding
• bleeding during labor

What are the causes and risks of the condition?

• she has had 6 or more births
• she is carrying two or more fetuses
• she previously had a cesarean section
• she is older than 35 years
• the placenta is large or abnormal

What can be done to prevent the condition?

There is no known way to prevent this condition.

How is the condition diagnosed?

Every woman with vaginal bleeding who might have this condition should be hospitalized and evaluated. The bleeding may become a hemorrhage without warning.

• a pregnancy ultrasound to check the placenta's location and rule out placenta abruptio, or separation of the placenta from the uterine wall
• continuous monitoring to assess the baby's well-being
• finding the baby's position by feeling the mother's abdomen. In about one-third of the cases of placenta previa, the baby is lying sideways or buttocks-first in the uterus.
• complete blood counts, or CBCs, to follow the mother's blood losses

In many cases, placenta previa causes no symptoms and detected only by pregnancy ultrasound in the early second trimester. In these cases, no symptoms may ever occur and the placenta later may become normally situated.

What are the long-term effects of the condition?

When a partial placenta previa is found early in pregnancy, it may be just be followed closely and, more times than not, a vaginal birth is possible.

Complete placenta previa usually calls for a cesarean birth when the unborn child's lungs are judged to be mature enough to allow the baby to survive outside the wound or if the mother starts to bleed heavily.

• suffers blood loss and shock
• gets an infection
• develops an embolism or blood clot
• must have a hysterectomy if the placenta will not separate from the uterus

While the mother is usually fine, birth trauma or a hemorrhage may harm the baby. In 15% to 20% of cases, the baby dies. This may be due to not getting enough oxygen in the uterus, prematurity, or other causes of fetal distress.

What are the risks to others?

Complications may harm the baby or cause its death.

What are the treatments for the condition?

Treatment varies depending on:

• the amount of bleeding
• the age of the unborn child
• the well-being of the baby
• whether the condition is complete or partial
• the position of the baby
• the mother's well-being
• whether labor has begun

In asymptomatic or mild cases, bedrest and no sexual intercourse may be advised. As the uterus grows, the placenta may move to a safer position.

Other treatment may include:

• using monitoring of the baby as needed
• giving the mother fluids through a vein
• monitoring the mother's vital signs, such as blood pressure, heart rate, and urine output
• observing, but not interfering with, the pregnancy if tests and signs suggest mother and baby are fine
• giving the mother blood transfusions to replace lost blood if the baby is immature, not in distress, and younger than 36 weeks gestation
• allowing a vaginal birth if the mother and baby are stable
• giving the mother a cesarean birth if she and the baby are not stable

Once an unborn child is 36 weeks gestation, a cesarean birth is generally done to avoid potential complications for mother and baby. First, though, tests may be done to check the maturity of the baby's lungs.

What are the side effects of the treatments?

The treatments for this condition may be lifesaving. Possible side effects should be weighed against the loss of life. Any surgery can cause bleeding and infection. Blood transfusions and medications can cause allergic reactions.

What happens after treatment for the condition?

• frequent blood counts, or CBCs
• blood tests to monitor the ability of her blood to clot
• vital signs

If the baby survives, he or she will be monitored carefully in the nursery.

How is the condition monitored?

A woman will be closely monitored throughout pregnancy to determine the status of the baby, as well as her own health.