Placenta Previa

The condition known as placenta previa is an uncommon pregnancy complication that can cause excessive bleeding before or during delivery. The placenta forms soon after conception and provides the oxygen and nutrients your baby needs to grow and develop. It also removes the waste from your baby’s blood. After the placenta has formed, it attaches itself to the wall of the uterus and forms an important connection between mother and baby via the umbilical cord.

In a normal pregnancy, the placenta attaches itself to the wall of the uterus in a location that is away from the cervix opening. Placenta previa occurs when the placenta attaches itself to the lower part of the uterine wall and either partially or completely covers the cervix.

When the cervix starts to open in preparation for labor, the placenta is detached, which usually triggers severe vaginal bleeding. Thankfully, placenta previa is almost always detected before it presents any kind of danger to mother or baby.

Placenta Previa Symptoms

The most common symptom of placenta previa is a bright red, yet painless bleeding from the vagina during the second or third trimesters. Some women experience light bleeding or spotting during their first trimester and at the beginning of their second, but this isn’t placenta previa, which happens toward the end of the second trimester, or at any time during the third trimester.

The amount of bleeding can vary. It usually stops, but almost always returns within days or weeks. Not all women have this symptom, however; about a third of women who have placenta previa do not bleed. Some women also experience contractions or cramps with placenta previa.

A doctor may in some cases suspect this condition if the baby is in the breech position.

Types of Placenta Previa

Placenta previa is classified as total, partial, or marginal. In total placenta previa, the placenta completely covers the cervix; with partial placenta previa, part of the cervix is covered; marginal placenta previa is when the placenta merely approaches the edge of the cervix.

Sometimes the placenta lies low in the uterus but doesn’t come close enough to the cervix for it to be considered a marginal placenta previa. This is known as a low-lying placenta. A low-lying placenta causes bleeding after delivery, but it doesn’t usually cause symptoms during the pregnancy.

Causes of Placenta Previa

Placenta previa occurs in about one out of every 200 pregnancies. Some of the things that can cause this condition include:

In many cases, placenta previa is caused by nothing more than happenstance. The placenta grows wherever in the uterus the embryo has implanted itself, so if the embryo implants in a low spot, a low-lying placenta—and possibly placenta previa—will result.

Complications of Placenta Previa

There are many complications that can occur with placenta previa. The biggest concern is the bleeding, which can lead to hemorrhaging during labor and delivery, maternal shock, or even death. In most cases, women with placenta previa will need to deliver via c-section. Preterm labor is also a possibility.

Placenta accreta can also occur. Placenta accreta happens when the placenta attaches too deeply and firmly to the uterine wall, making it difficult for the placenta to detach after delivery. This complication is very serious and almost always leads to a hysterectomy (removal of the uterus).

Diagnosis and Treatment

Placenta previa is usually diagnosed with an ultrasound examination at some point during the second trimester. In cases of marginal placenta previa, or in cases in which the condition is diagnosed early in the second trimester, treatment may not be necessary, as the continued growth of the uterus may move the point of placental attachment higher, away from the cervix.

If placenta previa is still present later in pregnancy, however, it is likely to complicate delivery. If your doctor suspects placenta previa, he or she will most likely want to monitor its development with regular ultrasound examinations. An MRI may also be employed to more accurately determine the exact location of the placenta.

Treatment will depend on a number of factors, not the least of which is the severity of the condition. If your bleeding is light, your doctor may simply recommend bed rest and abstinence from sex. If the condition is marginal, vaginal delivery of the baby may even be considered, although most cases require c-section delivery. In cases of heavier bleeding, however, especially if the placenta previa is total, hospitalization may be necessary, and the doctor may want to deliver the baby as soon as it is safe to do so, possibly as early as 36 weeks. In some cases doctors even administer steroids to speed the development of the baby’s lungs so that delivery can be sooner. The determination of whether the lungs are mature enough for the baby to be delivered is usually based on the results of amniocenteses.

This page was last updated on 06/2017

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