Chorioamnionitis, often shortened to chorio, is a bacterial infection that happens during pregnancy. It affects the membranes around the baby (the chorion and amnion) and the amniotic fluid. This condition is serious because it can lead to preterm labor, infections in the baby after birth, and other complications for the mother. Early detection and treatment are critical for both the pregnant person and the baby.
What Exactly Is Chorioamnionitis?
Chorioamnionitis is an infection of the fetal membranes and the amniotic fluid. Think of it as an infection inside the sac that holds the baby. It is a leading cause of preterm birth and can be dangerous if not treated quickly.
The infection is usually caused by bacteria that travel up from the vagina into the uterus. These bacteria are often the same types that cause other infections, like bacterial vaginosis or group B strep. Once the bacteria get inside the amniotic sac, they can multiply and cause inflammation.
Research published in journals like Obstetrics & Gynecology shows that chorioamnionitis occurs in about 1% to 4% of all term pregnancies. However, the rate is higher in preterm births, with some studies finding it in up to 10% of cases. The risk increases significantly the longer a woman’s water has been broken before delivery.
What Are the Main Causes and Risk Factors?
The most common cause is bacteria entering the uterus from the vagina. This happens more often when the protective barrier of the amniotic sac is broken. Prolonged rupture of membranes (your water breaking) for more than 18 hours before delivery is a major risk factor.
Other risk factors include:
- Internal monitoring during labor, such as fetal scalp electrodes or intrauterine pressure catheters
- Multiple vaginal exams after the water has broken
- Preterm labor or preterm premature rupture of membranes (PPROM)
- Infections like bacterial vaginosis or sexually transmitted infections
- A weakened immune system
- Smoking or using drugs during pregnancy
The American College of Obstetricians and Gynecologists (ACOG) notes that the risk also increases with the number of vaginal exams performed after the membranes rupture. Each exam can introduce bacteria higher up into the birth canal. This is why doctors limit exams once your water breaks.
What Symptoms Should You Watch For?
Symptoms can vary, but the classic signs of chorioamnionitis include a fever in the mother (usually over 100.4°F or 38°C). This is often the first and most reliable sign. Other common symptoms are a fast heart rate in the mother (over 100 beats per minute) and a fast heart rate in the baby (over 160 beats per minute).
The amniotic fluid may also smell bad or look cloudy or greenish. The uterus may feel tender to the touch. Some women report chills, sweating, or a general feeling of being unwell.
It is important to know that not all women with chorioamnionitis have obvious symptoms. In some cases, the only sign is a fever that develops during labor. The CDC states that prompt diagnosis is key because the infection can progress quickly. If you have a fever during labor, tell your healthcare team immediately.
How Is Chorioamnionitis Diagnosed and Treated?
Diagnosis is usually based on the symptoms and physical exam. There is no single perfect test. Doctors look for a fever plus at least two other signs, like a fast maternal heart rate, a fast fetal heart rate, uterine tenderness, or foul-smelling amniotic fluid.
Sometimes doctors will test the amniotic fluid. They may do a culture to see what bacteria are present. They may also check for high levels of certain proteins that indicate infection. However, treatment often starts based on symptoms alone, without waiting for test results.
Treatment is straightforward: antibiotics. The standard treatment is intravenous (IV) antibiotics given during labor. Common choices include ampicillin and gentamicin. The goal is to clear the infection in the mother and prevent it from spreading to the baby.
Delivery is also part of the treatment. Once chorioamnionitis is diagnosed, the baby usually needs to be delivered as soon as safely possible. This is because the infection will not fully resolve until the placenta and membranes are out of the body. Cesarean section may be necessary if labor is not progressing well, but vaginal delivery is often attempted first.
Comparison of Chorioamnionitis Signs in Mother vs. Baby
| Sign in Mother | Sign in Baby (Fetal) |
|---|---|
| Fever over 100.4°F | Fast heart rate over 160 bpm |
| Fast heart rate over 100 bpm | Low oxygen levels (seen on monitoring) |
| Uterine tenderness | Low muscle tone after birth |
| Foul-smelling amniotic fluid | Poor feeding or lethargy after birth |
| High white blood cell count | Temperature instability after birth |
What Are the Risks for the Baby and Mother?
For the baby, the biggest risk is developing an infection after birth. This can be a serious blood infection (sepsis), pneumonia, or meningitis. The baby may need to stay in the neonatal intensive care unit (NICU) for IV antibiotics and monitoring. Studies have found that babies born to mothers with chorioamnionitis are at higher risk for cerebral palsy and other long-term developmental issues, though the absolute risk is still low.
For the mother, the infection can spread to the bloodstream, causing sepsis. It can also lead to a uterine infection after delivery (endometritis), which requires more antibiotics. In rare cases, it can cause a blood clot in the pelvis or an abscess.
Some people report that chorioamnionitis can affect future pregnancies. Evidence indicates that having it once may slightly increase the risk of preterm birth in later pregnancies, but this is not a guarantee. The infection itself does not cause permanent damage to the uterus in most cases.
Common Misconceptions About Chorioamnionitis
A common myth is that chorioamnionitis is caused by something the pregnant person did wrong, like having sex or not being clean enough. This is false. The bacteria that cause it are normally present in many women’s vaginas and do not cause problems until they get into the uterus. It is not a hygiene issue.
Another misconception is that if your water breaks, you will definitely get chorioamnionitis. This is not true either. The risk increases with time, which is why doctors often recommend inducing labor if your water breaks and labor does not start on its own. But many women have their water broken for hours and never develop an infection.
Some people also believe that chorioamnionitis can be treated with oral antibiotics at home. This is incorrect. The infection requires IV antibiotics in a hospital setting, and the baby usually needs to be delivered. Home treatment is not safe.
Frequently Asked Questions
Can chorioamnionitis be prevented?
There is no guaranteed way to prevent it, but limiting vaginal exams after the water breaks and avoiding unnecessary internal monitoring can lower the risk. Treating vaginal infections early in pregnancy may also help.
Does chorioamnionitis always cause preterm labor?
No, it does not always cause preterm labor, but it is a leading cause. The infection triggers inflammation, which can start contractions and lead to early delivery. It can also occur at term.
How long after water breaking does chorioamnionitis develop?
Risk increases significantly after 18 hours of ruptured membranes. Most cases develop within 24 to 48 hours, but it can happen sooner or later depending on the bacteria and individual factors.
Can the baby be treated for chorioamnionitis before birth?
Antibiotics given to the mother cross the placenta and treat the baby before delivery. This is why prompt IV antibiotics are started as soon as the diagnosis is made, even before the baby is born.
