RELATED STORIES • Premature birth • Preeclampsia • Ectopic pregnancy • Placental abruption

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At the very beginning of pregnancy, the placenta begins to form. This circular, flat organ is responsible for providing oxygen and nutrients to your growing baby and removing waste products from your baby's blood. It attaches to the wall of your uterus and your baby's umbilical cord, forming a vital connection between you and your baby.

Early in pregnancy, the placenta may implant in the lower part of your uterus. However, as your uterus grows, the placenta usually moves up and away from the opening of your uterus, called your cervix. If it doesn't, it's called placenta previa.

This condition occurs in about one in 200 pregnancies, and it can be dangerous for both you and your baby. When the placenta covers the opening to your cervix, the placenta will detach from that part of your uterus as your cervix begins to thin and dilate in preparation for labor. This can cause severe vaginal bleeding.

In fact, most women with placenta previa experience moderate to heavy bleeding in the second half of pregnancy. This can be scary, but the bleeding will alert your health care provider to the condition — if it wasn't already detected by ultrasound. Then you can make plans to treat it.

Painless, bright red vaginal bleeding in the second half of pregnancy is the main sign of placenta previa. This bleeding usually occurs near the end of the second trimester or the beginning of the third. The amount of bleeding may range from light to heavy. And it may stop, but it nearly always recurs days or weeks later.

Some women with placenta previa experience contractions with bleeding. In addition, some women have light bleeding or spotting during the first trimester or early second trimester. Today, most cases of placenta previa are discovered by a routine ultrasound, done as part of your prenatal care, before any bleeding takes place.

Types of placenta previa
There are three types of placenta previa, but they all cause the same general signs and symptoms. An ultrasound is necessary to tell which form of the condition you have:

• Total placenta previa. In total placenta previa, the placenta completely covers the cervical opening.
• Partial placenta previa. In partial placenta previa, the placenta partly covers the cervical opening.
• Marginal placenta previa. In marginal placenta previa, the edge of the placenta is at the margin of the cervical opening. This form of placenta previa may not cause much bleeding, and it may be possible for your baby to make its way into the birth canal without any difficulty.

"Low-lying placenta" is another term related to placenta previa. This term is usually used to describe a placenta that lies low in the uterus but isn't quite close enough to the cervical opening to qualify as marginal placenta previa. This condition usually doesn't require treatment during pregnancy, but it may cause bleeding after delivery.

Placenta previa occurs when the embryo implants in the lower part of the uterus and then grows to cover the exit. Doctors and researchers don't understand why this happens. They hypothesize that the condition may be related to:

• Scars in the lining of the uterus (endometrium)
• A large placenta, such as in multiple pregnancy
• An abnormally shaped uterus

The most significant risk factor for placenta previa is a previous Caesarean birth. However, other factors may also increase your risk of developing the condition:

• Having had placenta previa before
• Having had other children
• Being age 35 and older
• Smoking
• Carrying twins, triplets or more

Previous uterine surgeries, such as myomectomy to remove uterine fibroids or dilation and curettage (D and C), in which the lining of the uterus is scraped for medical reasons, also seem to increase the risk of placenta previa.

If you're pregnant, seek regular prenatal care. If you experience any vaginal bleeding during your second or third trimester, call your health care provider right away. Your health care provider will want to perform an ultrasound to determine if you have placenta previa or some other condition.

If you have already been diagnosed with placenta previa, make sure that any health care provider you see during pregnancy is aware of the condition. This news will change the care you receive. For example, women with placenta previa usually don't have digital vaginal exams, because even the gentlest vaginal exam can trigger severe bleeding. For the same reason, you'll probably be advised to avoid sexual intercourse, exercise and certain medications. Make sure to discuss do's and don'ts with your doctor.

Placenta previa is discovered by ultrasound, during a routine prenatal appointment or after an episode of vaginal bleeding. The condition is almost always detected before a woman or her baby is in significant danger. But this is just another reason to get regular prenatal exams.

Diagnosis before 20 weeks of pregnancy
You may be told that you have a low-lying placenta or placenta previa before 20 weeks of pregnancy, based on the results of a routine ultrasound. This is fairly common. Up to 15 percent of pregnant women show some evidence of a low-lying placenta or placenta previa during their midpregnancy ultrasound. More than 90 percent of these cases spontaneously resolve before delivery, as the uterus grows and the placenta migrates away from the opening of the uterus.

However, your health care provider will monitor you closely to make sure that's the case. You may need extra ultrasounds to track the position of your placenta. The longer the placenta previa persists, the more likely it will be present at delivery.

Diagnosis after 20 weeks of pregnancy
Your health care provider may detect placenta previa late in pregnancy during an ultrasound for some unrelated reason. However, at this stage of pregnancy, vaginal bleeding is typically the tip-off.

If you experience vaginal bleeding in the second or third trimester, you'll need to go to your doctor's office or the hospital to determine the cause of the bleeding. Placenta previa is one of the first things your health care provider will look for. In most cases, an abdominal ultrasound can identify the location of your placenta, so your health care provider can quickly confirm or rule out this condition. But a definitive diagnosis may require a combination of abdominal ultrasound and transvaginal ultrasound — which requires a wand-like device placed inside your vagina.

If your health care provider suspects that you may have placenta previa, he or she won't do a vaginal exam, because it can trigger heavy bleeding. But you may undergo additional ultrasounds or magnetic resonance imaging (MRI) to detect the exact location of your placenta before delivery. These tests don't use radiation, like an X-ray, so there is no harm to your baby. If you have placenta previa, you may also be hooked up to monitors that check your baby's well-being.

If you have placenta previa, your doctor will monitor you and your baby carefully to reduce your risk of these serious complications:

• Massive bleeding (hemorrhage). One of the biggest concerns with placenta previa is the risk of severe vaginal bleeding, which can be heavy enough to cause maternal shock or even death.
• Premature birth. Placenta previa can lead to premature birth. Some women with severe bleeding actually need an emergency Caesarean birth sometime in the third trimester.
• Placenta accreta. In this condition, the placenta implants too deeply and firmly into the uterine wall, making it difficult for the placenta to spontaneously detach from the uterus after delivery. This can result in severe bleeding and the need for the surgical removal of the uterus (hysterectomy). This condition is rare, but it typically affects women with placenta previa or women who have had a previous Caesarean birth or some other uterine surgery.

Related conditions
These conditions are often grouped with placenta previa because they can cause vaginal bleeding in the late second or third trimesters. If you have vaginal bleeding late in your pregnancy, your health care provider will consider all three conditions before making a diagnosis.

• Placental abruption. Sometimes called abruptio placentae, this rare condition occurs when the placenta begins to separate from the inner wall of the uterus before birth. It can deprive the baby of oxygen and nutrients and cause heavy bleeding within the uterus that may be dangerous for the mother and her baby. Placental abruption can be a complication of placenta previa, but most abruptions happen in women without placenta previa.
• Vasa previa. In this rare condition, the umbilical cord develops in an abnormal place instead of in the center of the placenta, which allows the fetus's blood vessels to cross the cervix. This can result in rupture of the blood vessels, which causes life-threatening bleeding in the baby.

In general, treatment for placenta previa may include blood transfusions, bed rest and Caesarean delivery. But the details of your treatment depend on a range of factors, including:

• The amount of vaginal bleeding
• Whether the bleeding has stopped
• The gestational age of your baby
• Your health
• Your baby's health
• The position of the placenta and the baby

For marginal placenta previa or other forms with little or no bleeding
If you have marginal placenta previa that was diagnosed during a routine ultrasound or another form of placenta previa but little or no bleeding, you may be allowed to rest at home, rather than being admitted to the hospital. But your doctor will want to see you regularly, to monitor your blood levels, your baby's development and the position of your placenta.

The rules for bed rest depend on your individual situation. You may need to lie in bed, only sitting and standing when necessary. Or you may be advised to sit on the couch or in bed and to limit your activities. Either way, you'll need to avoid sexual intercourse, exercise and vaginal exams, which can trigger bleeding. You'll also want to avoid nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin and ibuprofen, unless your doctor recommends them, because these medications may contribute to bleeding. And you'll need to seek emergency medical attention if vaginal bleeding starts.

If your placenta doesn't cover the opening of your uterus, you may be allowed to attempt a vaginal delivery. But you'll be monitored closely, and you may need a Caesarean birth if there is heavy vaginal bleeding.

For severe bleeding
After an initial bleeding episode, women with placenta previa are often kept in the hospital, where a Caesarean birth is planned for as soon as the baby can be safely delivered. Ideally, your doctor will try to manage your condition until you've reached 36 weeks of pregnancy. In more severe cases, it may not be possible to wait, and you may need to undergo Caesarean birth earlier.

If bleeding is severe, you may need a blood transfusion to replace lost blood. If bleeding occurs before the last few weeks of your pregnancy, you may also need medications to prevent premature labor, as well as corticosteroids. These potent medications can help make your baby's lungs more mature in as little as 48 hours. Underdeveloped lungs are one of the biggest problems facing premature infants, so corticosteroids can be an important step in helping an immature baby prepare for life outside of the uterus.

For bleeding that won't stop
If bleeding starts and can't be controlled, an emergency Caesarean birth is necessary for the sake of the mother and baby — even if the baby is premature. You may also undergo urgent Caesarean birth if monitors show a problem with your baby's heart rate.

Pregnancy is supposed to be a time of awe and anticipation. Nine months of watching your belly grow and waiting to meet the little one inside. Nine months for picking out the softest quilt, the safest crib and the right rocking chair. A condition that could cause excessive bleeding before or during delivery isn't part of any mother's vision of the perfect pregnancy. Yet most women with placenta previa go on to deliver a happy, healthy baby — which is far better than a perfect pregnancy.

Still, if you're diagnosed with placenta previa, you're sure to be scared, anxious and worried about how your condition will affect your baby. Some of these strategies may help:

• Learn about placenta previa. Gathering information about your condition may help you feel less scared. Talk to your doctor, do some research on your own and ask your doctor to put you in touch with other women who have had placenta previa.
• Learn about Caesarean birth. Most women with placenta previa will have a Caesarean birth, so it's smart to talk about this procedure in advance. Take time to ask your doctor every question that comes to mind. If you're feeling disappointed that you won't deliver vaginally, talk about your feelings and ask about ways to make your birth as "natural" as possible, such as having your partner hold the baby close to you right away.
• Make the best of bed rest. If you're put on bed rest, fill your days by planning for your baby's arrival. Read about newborn care or purchase newborn necessities, either online or from catalogs. Or use your time to balance your checkbook, organize old photo albums or catch up on thank-you notes.
• Take care of yourself. Aside from following your treatment plan, you can't do anything to help your condition except to wait. But you can take steps to take care of yourself. Surround yourself with things that bring you comfort, such as prayer, a good book or a favorite pair of pajamas. Ask your mom to bring over her famous apple pie, or ask your best friends to stop by for a visit. Your partner, friends and family are likely looking for ways to help, so they'll be glad for a concrete suggestion.