Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at September 27, 2016

Chorioamnionitis is a complication of pregnancy that affects 1-4% of all births in the United States. This condition is also referred to as intra-amniotic infection and can cause a number of problems for the mother and baby.


Definition & Facts

Chorioamnionitis is an inflammation of the fetal amnion and chorion membranes, commonly known as the amniotic sac, typically due to a bacterial infection. This condition can occur before or during labor with the majority of cases occurring during labor.

It can cause stillbirths, premature births, and increase the need for cesarean sections. It is also known to cause chronic lung disease, brain injuries, including cerebral palsy, and other intellectual disabilities and physical disabilities, and sepsis in newborns. Mothers can experience infections, sepsis, excessive blood loss during labor and blood clots in their lungs and pelvis

Symptoms & Complaints

The most common indication of chorioamnionitis is a maternal fever greater than 100.4°F(38°C) that lasts for more than an hour or a high grade fever of 101°F (38.33°C) or more that lasts for any length of time. Another common symptom is a maternal heart rate greater than 100 beats per minute (BPM) and/or a fetal heart rate greater than 160 BPM.

Many women with this condition also have a uterus that is tender to the touch and complain of foul-smelling vaginal discharge. An increase in the white blood cell count may also indicate the presence of this infection.

Preterm labor or preterm, premature rupture of membranes (PPROM) may signal the presence of infection in the amniotic sac. PPROM may be experienced as a sudden gush of fluid from the vagina or a slow trickle. Since leaking urine also commonly happens during pregnancy, it can be hard to distinguish between the two.

The easiest way to differentiate between them is to monitor the rate at which the fluid leaks. Urine usually leaks sporadically, while amniotic fluid tends to leak at a constant rate. It is important to note that some women display no symptoms.


Chorioamnionitis occurs when bacteria moves to the uterus from the mother's lower genital tract (cervix and vagina). In pregnancies where the membranes have ruptured prematurely, the risk of infection increases as the length of time since rupture does.

This is because over 70% of women carry the bacteria most commonly responsible for causing chorioamnionitis in their lower genital tract and the membranes serving as a protective barrier have been compromised. Even with membranes intact, prolonged labor can cause amniotic infection because the uterus and vagina are exposed to each other for an extended time period.

Untreated group B streptococcus (GBS) is a main cause of this kind of infection. Other types of bacteria commonly known to cause chorioamnionitis are ureaplasma, E. coli and anaerobic bacteria, but it can be caused by many different types. Sexually transmitted disease and bacterial vaginosis are also causes of chorioamnionitis.

There are several risk factors associated with developing this condition. Mothers that are under 21 years of age, are of low socioeconomic status, are African-American, have a weakened immune system or have never been pregnant before have been shown to have an elevated risk.

Patients who smoke or abuse drugs and alcohol increase their probability of developing this condition. Frequent internal monitoring or excessive vaginal exams during labor with ruptured membranes increase the likelihood of infection. 

Diagnosis & Tests

Doctors are usually able to diagnose chorioamnionitis with a physical examination. Typically, a clinical diagnosis requires a maternal temperature greater than 100.4°F(38°C) along with two of the following: a painful uterus, an elevated maternal or fetal heart rate or amniotic fluid that has a foul odor or contains pus. Doctors will look for risk factors that might strengthen the diagnosis. Fetal and maternal heart rates will be monitored to check for elevated heart rates (tachycardia).

Some cases may require laboratory testing to confirm the diagnosis. A blood sample may be taken from the mother and tested for an elevated white blood cell count (leucocytosis). Leucocytosis on its own does not definitively prove the presence of chorioamnionitis, but it's a good indicator when paired with other symptoms.

A sample of amniotic fluid may be taken through a process called amniocentesis. Amniocentesis is an invasive procedure and results may not be available for up to three days, but it's sometimes necessary to determine whether preterm delivery is warranted. 

Treatment & Therapy

Once a diagnosis has been confirmed, treatment will begin immediately to reduce the occurrence and severity of complications. Since maternal fever has been shown to cause fetal brain damage, acetaminophen will be administered immediately to bring the mother's body temperature down. Patients will also be given antibiotics to fight the infection. If the infection is found before labor begins, antibiotics may be given orally to fight the infection until the mother carries the baby to full term and labor can be safely induced.

If the fetus is showing signs of distress, delivery will be immediate. During labor, antibiotics will be given to the mother through an IV and administration will continue until the infection is gone.

C-sections are between two and three times more probable for mothers with chorioamnionitis than for those without. A c-section will be necessary if vaginal delivery is taking or would take too long or if the mother's condition is deteriorating. Tests will be performed to see if the infection has spread to the baby; if so, antibiotics and any other necessary treatment will be administered to the newborn after delivery.

Most mothers and full-term babies respond well to antibiotics and don't need further treatment once the infection is gone. Premature babies are more likely to develop serious conditions that require long term care. 

Prevention & Prophylaxis

Prevention efforts include scheduling regular prenatal checkups, screening pregnant women for bacterial vaginosis and GBS, as well as minimizing the amount of internal monitoring performed during pregnancy and number of vaginal exams performed during labor.

Antibiotics may be given to mothers whose membranes have ruptured prematurely to prevent infection. Practicing safe sex and eliminating the use of douches and feminine sprays helps to prevent STD's and bacterial vaginosis, which are both causes of chorioamnionitis.