What is amnionitis?

Amnionitis, also known as chorioamnionitis or intra-amniotic infection, is an infection of the uterus, the amniotic sac (bag of waters), and in some cases, of the fetus.

Amnionitis is very rare, occurring in only about 2 to 5 percent of term-delivery pregnancies.

The uterus is normally a sterile environment (meaning that it does not contain any bacteria or viruses). However, certain conditions can make the uterus susceptible to infection.

When it does occur, infection of the uterus is a serious condition because it can’t be successfully treated without delivering the baby. This is a particular problem when the baby is premature.

What causes infection?

Bacteria that invade the uterus cause amnionitis. This usually happens one of two ways. First, bacteria can enter the uterus through the mother’s bloodstream. The second and more common route is from the vagina and cervix.

In healthy women, the vagina and cervix always contain limited numbers of bacteria. In certain people, however, these bacteria can cause infection.

What are the risks?

Risks for amnionitis include preterm labor, rupture of membranes, and a dilated cervix. These can allow bacteria in the vagina to gain access to the uterus.

Preterm premature rupture of membranes (aka PPROM, water breaking before 37 weeks) presents the highest risk for amniotic infection.

Amnionitis can also occur during normal labor. Factors that can increase the risk for amnionitis include:

  • a long labor
  • prolonged rupture of membranes
  • multiple vaginal exams
  • placement of fetal scalp electrodes
  • intrauterine pressure catheters

What are the signs and symptoms?

Symptoms of amnionitis are variable. One of the earliest signs can be regular contractions with cervical dilation. These symptoms together signify the start of preterm labor.

A woman will usually have a fever that ranges from 100.4 to 102.2ºF, according to The American College of Obstetricians and Gynecologists.

Additional symptoms may include:

  • flu-like feeling
  • abdominal tenderness
  • purulent cervical drainage (drainage that is foul-smelling or thick)
  • fast heart rate in mom
  • fast heart rate in baby (only detectable through fetal heart rate monitoring)

Laboratory tests may show a rise in the white blood cell count. If the infection is not treated, the baby may become sick and the fetal heart rate may increase. This is not obvious unless the mother is in a hospital and connected to a fetal heart rate monitor.

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

The mother can also become very sick and may develop sepsis. Sepsis is when the infection enters the mother’s bloodstream causing problems in other parts of the body.

This can include low blood pressure and damage to other organs. The bacteria release toxins that can be harmful to the body. This is a life-threatening condition. Treating amnionitis as quickly as possible can ideally keep this from happening.

How is amnionitis diagnosed?

The diagnosis of amnionitis in labor is based on the presence of fever, uterine tenderness, increased white blood cell count, and foul-smelling amniotic fluid.

Amniocentesis (taking a sample of amniotic fluid) is not used to diagnose amnionitis during normal labor. This is usually too invasive when a mom is in labor.

How is amnionitis treated?

Antibiotics should be given as soon as possible after the diagnosis is made to lower the risk for both the mother and fetus. A doctor will usually prescribe these medicines to administer intravenously.

Supportive therapy such as eating ice chips, cooling the room, or using fans, can help to cool a woman’s temperature.

When a doctor diagnoses an infection during labor, efforts should be made to shorten labor as much as possible. They may prescribe oxytocin (Pitocin) to strengthen contractions. Amnionitis can also be a cause of dysfunctional labor, despite the use of oxytocin.

Doctors don’t usually recommend a cesarean delivery (C-section) for a mom just because she has amnionitis.

What’s the outlook for amnionitis?

Recognizing and seeking treatment for amnionitis is vital to a good outcome for mom and baby. A woman should always call her doctor if she has a fever that lasts more than a few hours.

If she doesn’t seek treatment, the infection could progress. Sepsis or fetal complications can result. With antibiotics and potentially augmenting labor, a woman and her baby can experience a positive outcome and reduce the risks for complications.