Chorioamnionitis is a bacterial infection that occurs before or during labor. The name refers to the chorion (outer membrane) and the amnion (fluid-filled sac). These membranes surround the fetus. Chorioamnionitis occurs when bacteria infect the chorion, amnion, and the fluid around the fetus (amniotic fluid).

The condition can lead to a preterm birth or serious infection in the mother and the baby. Chorioamnionitis is most commonly seen in preterm births. It occurs in approximately 2 to 4 percent of full-term deliveries.

Chorioamnionitis is also known as amnionitis or intra-amniotic infection.

Chorioamnionitis usually develops due to an infection. The infection can occur when bacteria that are normally present in the vagina ascend into the uterus, where the fetus is located. The amniotic fluid and placenta — as well as the baby — can become infected. E. coli, group B streptococci, and anaerobic bacteria are the most common causes of chorioamnionitis.

Chorioamnionitis doesn’t always cause symptoms, but some women may experience:

  • a fever
  • rapid heartbeat
  • uterine tenderness
  • discolored, foul-smelling vaginal discharge

The most common risk factors for chorioamnionitis include:

  • young maternal age (less than 21 years old)
  • low socioeconomic status
  • first pregnancy
  • long labor
  • membranes that are ruptured (the water has broken) for an extended period of time
  • premature birth
  • multiple vaginal examinations during labor (only in women with ruptured membranes)
  • pre-existing infections of the lower genital tract
  • excessive fetal or uterine monitoring

You may be more likely to develop chorioamnionitis if you have one or more of these risk factors.

Chorioamnionitis is usually considered a medical emergency. The condition can lead to serious complications, including:

  • bacteremia (infection in the bloodstream)
  • endometritis (infection in the lining of the uterus)
  • need for cesarean delivery
  • heavy blood loss with delivery
  • blood clots in the lungs and pelvis

Bacteremia occurs in 3 to 12 percent of infected women.

Chorioamnionitis also increases the need for a cesarean delivery. Up to 8 percent of women who have a cesarean delivery develop a wound infection, and approximately 1 percent develop a pelvic abscess (collection of pus in the pelvis). Maternal death due to infection is extremely rare.

Babies delivered to mothers with chorioamnionitis are in danger of serious complications. Chorioamnionitis can lead to an infection of the lining of the brain and spinal cord, called meningitis. However, this occurs in less than 1 percent of infants who are delivered to term.

About 5 to 10 percent of infected babies may also develop pneumonia (lung infection) or bacteremia. However, bacteremia is more common in preterm infants. In rare cases, the complications associated with chorioamnionitis can be life-threatening to preterm infants.

Your doctor can usually diagnose chorioamnionitis by performing a physical examination. Laboratory tests can confirm a chorioamnionitis diagnosis.

An amniocentesis may be necessary if you’re in preterm labor. In this prenatal test, a small amount of amniotic fluid is removed for testing. You may have chorioamnionitis if the amniotic fluid has a low concentration of glucose (sugar) and a high concentration of white blood cells and bacteria.

Once you’re diagnosed with chorioamnionitis, you’ll be treated immediately to prevent complications. Early treatment can bring down your fever, shorten your recovery time, and lower your baby's risk of infection and complications.

Antibiotics are commonly used to treat chorioamnionitis. They’re usually given through an IV and continued until you’ve delivered your baby. You may receive some of the following antibiotics:

Once the infection is gone, you can stop using antibiotics and leave the hospital. Most people don’t require oral antibiotics on an outpatient basis.

The long-term outlook for mothers with chorioamnionitis is excellent. Future fertility is rarely compromised. The outlook for infants delivered to infected mothers is also very good. However, some babies, particularly those who are preterm, may have long-term complications. These complications can include lung disease or impaired brain function.

Your doctor will make every effort to prevent the infection from developing in the first place. They can do this in several ways, such as:

  • screening you for bacterial vaginosis (vaginal inflammation) in your second trimester
  • screening you for group B streptococcal infection once you reach 35 to 37 weeks of pregnancy
  • reducing the number of vaginal examinations they perform during labor
  • minimizing the frequency of internal monitoring

It’s important to attend regular checkups with your doctor and address your questions and concerns.