What Is Chorioamnionitis?

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Chorioamnionitis—also known as amnionitis or intrauterine infection—is a serious bacterial infection of the membranes that surround the fetus and the amniotic fluid during pregnancy. The name refers to the “chorion” (the outermost membrane around the fetus) and the “amnion” (the innermost membrane, or the fluid-filled sac).

Chorioamnionitis can lead to preterm birth or serious infections in the mother and the fetus. In most cases, this may mean the fetus has to be delivered as soon as possible. The infection complicates as many as 40 to 70% of preterm births and 1 to 13% of term births.

Recognizing and seeking treatment for chorioamnionitis can reduce the risk of complications and provide a good outcome for you and your baby.

This article covers the symptoms, causes, diagnosis, and treatment of chorioamnionitis.

Pregnant African American mother holding her stomach


JGI/Tom Grill/Getty Images

Signs and Symptoms

Symptoms of chorioamnionitis are variable. Sometimes pregnant people don’t display symptoms, especially if they develop the condition early in their pregnancy.

Symptoms may include:

  • A flu-like feeling
  • A fever above 100.4 F (fever is not common during pregnancy and should always be investigated)
  • Rapid maternal heartbeat (the fetus might also have a rapid heartbeat)
  • Sweating
  • A uterus that is painful or tender to the touch
  • Vaginal discharge that has an unusual smell

Without treatment, you may go into preterm labor. In rare cases, a serious infection could lead to fetal death.

Symptoms and Labor

Symptoms may not become apparent until you are in labor. The majority of pregnant people presenting with chorioamnionitis are in labor or have rupture of the membranes (when their "water breaks").

Causes

Chorioamnionitis is caused by a bacterial infection that usually starts in the organs of the reproductive system and the urinary system. Specifically, the infection can start in the vagina, anus, or rectum and move into the uterus where the fetus is developing.

The womb, amniotic fluid, and the environment surrounding the baby can then become infected with bacteria.

Common types of bacteria that cause chorioamnionitis include the following:‌

The infection causes the membranes to become inflamed, which may trigger preterm contractions. It could also cause the water to break early (also known as preterm premature rupture of the membranes, or PPROM). 

Preterm Labor and Chorioamnionitis

Choroamionitis occurs in 94% of preterm deliveries of between 21 and 24 weeks gestation.

Diagnosis

Chorioamnionitis is most often diagnosed by a physical exam and after a discussion of the symptoms. Your healthcare provider may order blood culture and urine tests as well. These tests check for the presence of bacteria in your body. A complete blood count (CBC) checks your white blood cell count and other markers.‌‌ Your healthcare provider may also use an ultrasound to check on the health of the fetus.

If you are suspected of having chorioamnionitis before you go into labor, your healthcare provider may order an amniocentesis and test the amniotic fluid for signs of bacteria. 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. While chorioamnionitis can be diagnosed with amniocentesis and by testing the amniotic fluid, it is not routinely done.

Several other conditions will be ruled out before a diagnosis of chorioamnionitis. Infections occurring outside of the uterus can cause fever and abdominal pain, either during or in absence of labor, including:

If chorioamnionitis is suspected during labor, your healthcare provider may make a diagnosis and opt for treatment based on clinical symptoms.

Treatment

Because chorioamnionitis is a serious infection, it needs immediate treatment. Antibiotics are the most common treatment to get the infection under control. They’re usually given intravenously (via an IV drip). You may also receive acetaminophen to reduce your body temperature.

If your baby has picked up the infection and the baby’s condition isn’t stable, your healthcare provider may suggest inducing labor. Once your baby is born, the baby will also receive direct IV antibiotics.

Intra-amniotic (occurring within the amniotic sac) infection alone is rarely, if ever, an indication for cesarean delivery.

Risk Factors

Your age, physical well-being, lifestyle, or underlying health conditions could increase your risk of developing chorioamnionitis.

‌Other common risk factors include:‌

  • Your membranes have ruptured early.
  • You have a very long labor (called failure to progress).
  • You have had frequent vaginal examinations during labor.
  • You have a disease transmitted by sex. 
  • You have a separate vaginal, urinary, or placental infection.
  • You’re having your first child.
  • You are given epidural anesthesia during labor. 
  • You have a short cervix.
  • You use drugs, tobacco, or alcohol.
  • You are immunocompromised.‌

One or more of these risk factors may put you at risk to develop chorioamnionitis.

Complications

Pregnant people who have a serious case of chorioamnionitis—or one that goes untreated—might develop significant complications, including:

  • Bacteremia (infection in the bloodstream, which occurs in 5 to 10% of chorioamnionitis cases)
  • Endometritis (an infection of the endometrium, the lining of the uterus)
  • Blood clots in the pelvis and lungs
  • Postpartum hemorrhage

Your baby may develop the following short-term or long-term complications:‌

‌‌Preterm newborns have immature immune systems, and their immune systems may be further compromised by various other factors associated with preterm birth. If the infection is widespread long before your healthcare provider diagnosis it, your pregnancy could result in stillbirth (the birth of a dead fetus) or death after delivery.

Prevention

Sometimes, you can prevent chorioamnionitis, but often this condition will develop regardless of preventive measures. 

Routine checkups may identify vaginal inflammation or early signs of infection. During your last month of pregnancy, your healthcare provider will order blood tests that check for Group B strep—common bacteria that cause chorioamnionitis. 

If you display any of the signs and symptoms, reach out to your healthcare provider to schedule a visit. It’s important to attend regular checkups with your practitioner in order to address your questions and concerns.

Summary

Chorioamnionitis—also known as amnionitis or intrauterine infection—is a bacterial infection of the membranes that surround the fetus in the uterus and the amniotic fluid during pregnancy.

A Word From Verywell

Recognizing and seeking treatment for chorioamnionitis is vital to a good outcome for you and your baby. When you are pregnant, you should always call your healthcare provider if you have a fever that lasts more than a few hours as it may be a sign of infection.

If left untreated, the infection could pose a serious risk to both you and your baby. But with prompt treatment, you can reduce the risks for complications.

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