Placenta previa is a condition that occurs when the placenta remains low in the uterus and covers or lies next to the internal cervical os, the opening to the cervix. The cervix is the portion of the uterus that dilates during the first stage of labor allowing delivery of a baby.

This condition can cause bleeding that can become severe and result in serious complications, such as massive bleeding (hemorrhaging), premature birth and, in rare cases, death of the mother or baby. It occurs in approximately 1 in 200 births, according to the National Institutes of Health (NIH).

There are several types of placenta previa:

• Total placenta previa. The placenta covers the entire internal cervical os.
  
  
• Partial placenta previa. The placenta covers part of the internal cervical os.
  
  
• Marginal placenta previa. The placenta is near, but not covering, the internal cervical os.

The cause of placenta previa has not been identified, but some possible causes are scars in the uterine lining (endometrium) and an abnormally large placenta resulting from a multiple gestation. Risk factors include having had previous Caesarean sections (C-section) deliveries and uterine surgeries.

The most common symptom of placenta previa is painless vaginal bleeding during the second half of pregnancy. Some women experience spotting earlier in the pregnancy and some experience no symptoms at all.

Placenta previa is usually diagnosed with an abdominal ultrasound performed during a routine prenatal examination by an obstetrician-gynecologist (ObGyn). A transvaginal ultrasound or MRI (magnetic resonance imaging) may be performed to pinpoint the location of the placenta in the uterus.

Treatment for placenta previa varies depending on the severity of the bleeding, age of the fetus and other factors. Women who are experiencing little or no bleeding may be prescribed bed rest. Women with more severe bleeding are usually hospitalized. Most women with placenta previa give birth by C-section.

Placenta previa is a condition that occurs during pregnancy when the placenta lies low in the uterus and partially or completely covers the internal cervical os (the small opening of the cervix that dilates during the first stage of labor).

Shortly after conception, the placenta (a flat, circular organ) attaches to the inner wall of the uterus and the baby’s umbilical cord. It transfers oxygen and nutrients from the mother’s blood to the fetus. It also transfers waste from the baby’s blood to the mother’s blood, where the mother’s kidneys dispose of the waste. The placenta also protects the baby from infection and produces hormones that trigger labor and delivery.

Under normal circumstances, the placenta migrates away from the mother’s cervix as the uterus grows. In women with placenta previa, this does not happen. The abnormally positioned placenta can block the birth canal, obstructing the baby’s exit from the uterus. As the cervix dilates and thins in preparation for labor, blood vessels connecting the placenta to the uterus can tear and cause bleeding.

The bleeding can become severe and pose serious complications to the mother and baby, including:

• Infection. The risk of infection to the mother and baby increases with placenta previa.
  
  
• Blood clots (clumps that result from coagulation of the blood). Women with placenta previa are at a higher risk of getting blood clots.
  
  
• Premature birth (birth of an infant before 37 weeks of gestation). Placenta previa can result in premature labor and delivery.
  
  
• Massive bleeding (hemorrhaging). Placenta previa can cause massive vaginal bleeding due to the placenta separating from the uterine wall during labor. Women experiencing massive blood loss may require a blood transfusion. Hemorrhaging can also cause the mother or baby to go into shock (a life-threatening condition that occurs when the body is not getting adequate blood flow). In rare cases, it can result in the death of the mother or baby.

Placenta previa occurs in approximately 1 in 200 births, according to the National Institutes of Health (NIH).

There are several placental conditions that are related to placenta previa. They can also cause vaginal bleeding in the second and third trimesters. These conditions include:

• Placental abruption (placenta abruptio). A condition in which the placenta breaks away from the uterine wall. This condition can deprive the baby of oxygen and nutrients and cause heavy bleeding. It can be a complication of placenta previa, but usually occurs in women without it.
  

• Placenta accreta. A condition in which the placenta implants too firmly into the uterine wall. Placenta accreta is most common in women with placenta previa. It can cause vaginal bleeding and result in premature birth. This condition most commonly occurs in women who have had previous uterine surgery. Some women with placenta accreta need a hysterectomy, as this may be the only way to stop the massive bleeding that can occur with this condition.
  
  
• Vasa previa. A condition in which the umbilical cord develops in an abnormal position. This allows the baby’s blood vessels to cross the cervix, resulting in rupture. This can cause life-threatening bleeding in the baby.

There are three types of placenta previa, but all result in approximately the same signs and symptoms. These types are:

• Total placenta previa (placenta previa centralis). The internal cervical os (the small opening of the cervix that dilates during the first stage of labor) is completely covered by the placenta.
  
  
• Partial placenta previa (placenta previa partialis). The internal cervical os is partly covered by the placenta.
  
  
• Marginal placenta previa (placenta previa marginalis). The placenta is near, but not covering, the internal cervical os. This may not cause as much bleeding as the other types.

There is another condition related to placenta previa called low-lying placenta. This term is used to describe several circumstances:

• Placenta previa experienced in the second trimester.
  
  
• Placenta that lies low in the uterus but whose proximity to the internal cervical os has not been determined.
  
  
• The edge of the placenta lies within 2 to 3 centimeters (0.8 to 1.2 inches) of the internal cervical os.

Although the exact cause of placenta previa is not known, there are several possible causes that have been identified by health experts. These include:

• Scars in the endometrium, the lining of the uterus
• Large placenta, commonly found in women having multiple births
• Unusually shaped uterus
• Abnormally formed placenta

Several risk factors for placenta previa have been identified. These include:

• Past incidence of placenta previa. Women who have experienced the condition in past pregnancies are more likely to experience it again.
  
  
• Age. Women ages 35 and older have a higher incidence of placenta previa.
  
  
• Past Caesarean sections (C-sections). The more C-sections (removal of the fetus through an incision made through the uterus and usually through the abdominal wall) a woman has, the greater the incidence of placenta previa.

• Multiple gestations. Women carrying twins, triplets or more babies are more apt to have placenta previa because of a larger placenta.
  
  
• Multiple pregnancies. The more children a woman has, the greater the likelihood of developing placenta previa with future pregnancies.
  
  
• Previous operations on the uterus. Past surgeries, such as surgery to remove uterine fibroids (e.g., myomectomy) or dilation and curettage (D&C). This is a procedure in which the entrance to the woman’s uterus is expanded and tissue samples are removed from the uterine lining. Physicians commonly perform a D&C procedure after a miscarriage or a medical abortion.
  
  
• Cigarette smoking. Smoking decreases the amount of oxygen to the fetus, causing a larger placenta to grow. A larger placenta is more likely to grow low in the uterus.
  
  
• Cocaine use. Women who use cocaine during pregnancy are more apt to develop placenta previa.
  
  
• High altitude. Women who live in high-elevation areas have a greater incidence of placenta previa.
  
  
• Male fetus. Women carrying boys are more likely to develop placenta previa. This may be due to the typically larger size of a male fetus.

In addition, women who use assisted reproductive technology (ART), such as in vitro fertilization (IVF), to achieve pregnancy may be at increased risk of developing placenta previa, according to a recent large-scale study.

Many cases of placenta previa are diagnosed during a regular prenatal examination, when an obstetrician-gynecologist (ObGyn) conducts a vaginal examination and performs an abdominal ultrasound (a test that uses sound waves to produce images of the body’s organs).

Ultrasounds are commonly performed as a routine part of prenatal care. When women receive routine prenatal care during pregnancy, placenta previa is usually detected before it poses a danger to the mother or child.

It is common for women to be diagnosed with placenta previa in the first 20 weeks of pregnancy. In most cases, the condition will resolve itself when the placenta migrates away from the cervix.

After 20 weeks of pregnancy, placenta previa may be diagnosed when the women experiences vaginal bleeding. When women experience bleeding in the later stages of pregnancy, a vaginal examination is usually not performed because it can trigger heavy bleeding.

Instead, the physician may conduct an abdominal ultrasound or a transvaginal ultrasound (a procedure in which a probe that emits sound waves is inserted into the vagina to produce a picture of body tissue).

To identify the precise location of the placenta, the physician may perform an MRI (magnetic resonance imaging), a test that helps physicians diagnose diseases of numerous organs and vessels.

The treatment of placenta previa depends on several factors, including:

• Severity of vaginal bleeding
• Whether bleeding has stopped
• Age of fetus
• Mother’s health
• Health of the fetus
• Position of fetus and placenta

In cases of marginal placenta previa or where women experience little or no bleeding, some women may be permitted to stay home and be treated with bed rest. Others may be required to be admitted to a hospital for treatment.

Requirements of bed rest vary among individuals. Some women may be required to remain lying in bed, sitting and standing only when necessary. Others may be permitted to sit and stand more frequently, but are required to limit overall activity, such as housework and heavy lifting.

Women on bed rest should avoid sexual intercourse, exercise and vaginal examinations because these activities can cause heavy bleeding. It is also recommended that women on bed rest continue with regular physician visits for continued monitoring of the condition.

Most women with placenta previa will need to have a Caesarean section (removal of the fetus through an incision made into the uterus and usually through the abdominal wall) to deliver the baby. If the placenta is not covering the cervix, some women may be permitted to attempt a vaginal delivery. However, if heavy bleeding occurs during the vaginal delivery, a C-section may be necessary to protect the health of the mother and her baby.

Women experiencing more severe bleeding are often required to stay in the hospital until they can safely deliver the baby. In addition, women who experience severe blood loss may need a blood transfusion to replace the lost blood. Due to the increased risk of excessive blood loss, patients may choose to a have family member or friend donate blood beforehand in case a transfusion is needed as they may feel more comfortable receiving blood from someone they know (directed donor blood).  

Physicians usually attempt to manage the condition until a woman has reached 36 weeks of pregnancy, after which a C-section is planned. If bleeding starts and cannot be controlled or a problem with the baby’s heart rate is detected, an emergency C-section may be performed even if the baby is premature.

Women with placenta previa may be treated with a corticosteroid medication (a drug that helps speed the development of the fetus’ lungs). This helps improve the fetus’ survival rate outside the womb. At 36 weeks of pregnancy, a physician may perform an amniocentesis (a test in which fluid is removed from the amniotic sac with a needle and syringe inserted through a pregnant woman’s abdomen) to determine whether the baby’s lungs are mature. If the lungs are mature, a C-section may be performed at this point of the pregnancy.

Placenta previa cannot be prevented, but women can lower their risk by refraining from smoking or using cocaine. In addition, proper prenatal care is important for both the mother and the baby. Women who experience bleeding during pregnancy should contact a physician immediately. Early detection of the condition can reduce the risk of complications to the mother and child.

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor or healthcare professional the following questions about placenta previa:

1. Am I at risk for placenta previa?
   
   
2. What tests will be used to diagnose placenta previa?
   
   
3. What type of placenta previa do I have?
   
   
4. How will my form of placenta previa affect my baby?
   
   
5. Can the condition change or become worse?
   
   
6. Can placenta previa cause other medical problems?
   
   
7. What are my treatment options?
   
   
8. If I’m put on bed rest, how long will it likely last?
   
   
9. What are the restrictions with my condition?
   
   
10. How will placenta previa be monitored during my pregnancy?
    
    
11. Which symptoms can indicate a medical emergency?
    
    
12. How will I know if I need a blood transfusion?
    
    
13. What are the chances that I can have a vaginal delivery?
    
    
14. When will I know if I need to have a C-section?
    
    
15. What are the chances that I may need a blood transfusion? Can I have a relative donate blood for my transfusion?
    
    
16. Am I at greater risk for this condition in future pregnancies?