Chorioamnionitis (Intraamniotic Infection)

What happens in chorioamnionitis

During pregnancy the amniotic sac and the plug of mucus in the cervix keep the uterus mostly free of bacteria. When the membranes rupture, or the cervix opens in labor, bacteria from the vagina can climb upward into the amniotic fluid. This is called ascending infection.

Infection is usually caused by a mix of organisms: genital mycoplasmas such as Ureaplasma, anaerobic bacteria, E. coli and group B streptococcus. Rarely, bacteria reach the uterus through the bloodstream, as with Listeria from contaminated food.

In 2017 the American College of Obstetricians and Gynecologists (ACOG) recommended the name intraamniotic infection, sometimes shortened to "Triple I" (intrauterine inflammation or infection or both). Many doctors still say chorioamnionitis.

Symptoms

• Fever of 38 °C (100.4 °F) or higher, the core sign
• Fast maternal heart rate, over 100 beats per minute
• Fast fetal heart rate, over 160 beats per minute on the monitor
• Tender uterus between contractions
• Foul-smelling or cloudy amniotic fluid or vaginal discharge
• Chills and sweating

Some infections, particularly earlier in pregnancy, cause few symptoms and are found only when preterm labor starts or the placenta is examined after birth (histologic chorioamnionitis).

Risk factors

• Prolonged rupture of membranes, especially longer than 18 hours
• Long labor, especially a long second (pushing) stage
• Several vaginal exams after the waters have broken
• Preterm premature rupture of membranes (waters breaking before 37 weeks)
• Internal monitoring with a fetal scalp electrode or uterine pressure catheter
• First pregnancy
• Group B strep colonization, bacterial vaginosis or other genital tract infections
• Meconium-stained fluid
• Smoking, alcohol or drug use in pregnancy
• A previous episode of chorioamnionitis

How it is diagnosed

Diagnosis in labor is mostly clinical. ACOG defines suspected intraamniotic infection as:

• a maternal temperature of 39.0 °C (102.2 °F) or higher once, or 38.0 to 38.9 °C (100.4 to 102.0 °F) on two readings 30 minutes apart, plus
• at least one of: fetal heart rate over 160 for 10 minutes or more, maternal white blood cell count over 15,000 without steroids, or pus-like fluid from the cervix

Fever alone in labor, especially with an epidural, can have other causes, so the whole picture matters.

Before labor, when the diagnosis is unclear, an amniocentesis (a sample of fluid taken with a needle) may be tested for bacteria, white cells and low glucose. After birth, the placenta and membranes can be examined under a microscope to confirm it.

Treatment

For the mother

• IV antibiotics started as soon as infection is suspected. The usual combination is ampicillin plus gentamicin. If a cesarean is needed, a drug covering anaerobic bacteria, such as clindamycin or metronidazole, is added.
• Delivery. Antibiotics alone cannot cure an infection in the uterus while the baby and membranes remain inside. Chorioamnionitis by itself is not a reason for a cesarean. Labor is usually sped up, and a cesarean is done only for the usual obstetric reasons.
• Fever control with acetaminophen (paracetamol), which also helps lower the baby's heart rate.

Antibiotics are often stopped after a vaginal birth if the mother is improving, or continued for a short time after a cesarean or if fever persists.

For the newborn

A pediatric team is usually present at the birth. Depending on the gestation and how the baby is doing, the baby is monitored closely, has blood tests and a blood culture, or receives IV antibiotics for possible neonatal sepsis. Many hospitals use a risk calculator for babies born at 35 weeks or later, which reduces unnecessary antibiotic use.

Complications

For the mother

• Postpartum hemorrhage from a tired, inflamed uterus that does not contract well
• Infection of the uterine lining after birth (endometritis) and wound infection after cesarean
• More need for cesarean delivery because labor progresses poorly
• Rarely, sepsis or blood clots in pelvic veins

For the baby

• Early-onset sepsis, pneumonia or meningitis
• Preterm birth and its complications, since infection is a major trigger of preterm labor
• In preterm babies, higher risks of chronic lung disease, bowel inflammation (necrotizing enterocolitis) and brain injury, including cerebral palsy

Most full-term babies exposed to chorioamnionitis do well, especially with prompt treatment.

Prevention

• Group B strep screening at 36 to 37 weeks, with IV antibiotics in labor if positive
• Antibiotics after preterm waters breaking, which delay delivery and reduce infection
• Induction of labor after waters break at term rather than waiting many days
• Limiting vaginal exams once the membranes have ruptured
• Treating bacterial vaginosis when it causes symptoms, and avoiding high-risk foods for Listeria (unpasteurized milk and soft cheeses, deli meats unless heated)

Frequently asked questions

What causes chorioamnionitis?

It is usually caused by bacteria that normally live in the vagina moving up into the uterus after the waters break or as the cervix opens in labor. Infections usually involve several types of bacteria, including Ureaplasma, E. coli, anaerobes and group B strep. Long labor and long-ruptured membranes raise the risk.

How does chorioamnionitis affect the baby?

Most full-term babies are fine after prompt treatment. The main risks are newborn infection, such as sepsis, pneumonia or meningitis. In preterm babies the inflammation is also linked to lung disease, bowel problems and brain injury, so they are monitored especially closely after birth.

Does chorioamnionitis mean I need a C-section?

No. Chorioamnionitis alone is not a reason for cesarean delivery. Doctors give IV antibiotics and usually help labor progress. A cesarean is done only for standard obstetric reasons, such as labor that stops progressing or concerns about the baby's heart rate.

Can chorioamnionitis happen without the waters breaking?

Yes, though it is less common. Bacteria can sometimes pass through intact membranes, especially with a short or open cervix. Listeria can reach the placenta through the bloodstream. These infections often cause few symptoms and may first show up as preterm labor.

Will I get chorioamnionitis again in a future pregnancy?

Having it once raises the chance of it happening again, but most people do not have it in their next pregnancy. Tell your prenatal team about it so they can manage risk factors, such as screening and treating infections and planning care if your waters break early.