Chorioamnionitis (also called amnionitis or intra-amniotic infection) is a bacterial infection that occurs either before or during labor. The name refers to the outer membrane (chorion) and the fluid-filled sac (amnion) that encloses the embryo. Chorioamnionitis affects between 1 and 10% of women at term and up to 33% of patients who deliver preterm.
Chorioamnionitis usually develops when bacteria that are part of the normal vaginal flora ?ascend? into the uterine cavity. The amniotic fluid and placenta, as well as the baby, become infected. E. coli, group B streptococci, and anaerobic bacteria are the most common causes of chorioamnionitis, though, E. coli and group B streptococci are also the two most common causes of infection in newborns.
The most common risk factors for chorioamnionitis include:
- young age (e.g., less than 21 years old);
- low socioeconomic status;
- first pregnancy;
- long labor;
- prolonged rupture of the membranes (bag of waters);
- rupture of membranes at an early gestational age;
- multiple vaginal examinations during labor (only in women with ruptured membranes);
- pre-existing infections of the lower genital tract (bacterial vaginosis and group B streptococcal infection); and
- internal fetal and uterine monitoring.
The more of these risk factors you have, the more likely you are to develop chorioamnionitis.
Chorioamnionitis can lead to serious complications in both mother and baby and is usually considered a medical emergency. Bacteremia, labor abnormalities, need for cesarean delivery, and heavy blood loss with delivery are the most common complications. Bacteremia (infection in the bloodstream) occurs in 3 to 12% of infected women. In addition, chorioamnionitis also dramatically increases the need for a cesarean section (C-section) delivery. Up to 8% of women who undergo C-section develop a wound infection, and approximately one percent develop a pelvic abscess (collection of pus in the pelvis). Fortunately, maternal death due to infection is extremely rare.
Babies delivered to mothers with chorioamnionitis are in danger of a number of serious complications:
- about 5 to 10% of infected babies develop pneumonia (lung infection) or bacteremia (however, this is more common in preterm infants);
- less than 1% of term infants and a slightly higher percentage of preterm infants develop meningitis (infection of the lining of the brain and spinal cord); and
- although death in term babies is very unusual, up to 15% of infected preterm infants die because of the infection or other complications such as respiratory distress syndrome and bleeding into the brain.
In most cases, your doctor can diagnose chorioamnionitis due to fever in the mother and an increased heart rate in both the mother and her baby. In more severely ill patients, uterine tenderness and discolored, foul-smelling amniotic fluid (another indication of infection) may be present.
Laboratory confirmation of a chorioamnionitis diagnosis is not routinely necessary in term patients who are progressing to delivery. However, if you are in preterm labor, an amniocentesis may be necessary. If the amniotic fluid has a low concentration of glucose and a high concentration of white blood cells and bacteria, the diagnosis is confirmed.
If you are diagnosed with chorioamnionitis, you are treated immediately to prevent complications, usually with intravenous antibiotics that are safe with pregnancy and breast-feeding. Early treatment helps bring down your fever, shorten your need for hospitalization, and lower your baby's risk of infection and related dangers. Acetaminophen can also be used to reduce fever. Some considerations about medications used to treat chorioamnionitis include:
- The most common treatment for chorioamnionitis is the combination of ampicillin (Principen) or penicillin (PenVK) plus gentamicin (Garamycin). These antibiotics specifically target the two organisms-group B streptococci and E. coli -most likely to cause neonatal infection.
- If you are allergic to ampicillin or penicillin, your doctor prescribes clindamycin (Cleocin).
- If you require cesarean delivery, a drug with activity against anaerobic organisms is added to the antibiotics, usually clindamycin or metronidazole (Flagyl).
- Several broad-spectrum antibiotics-such as cefoxitin, cefotetan, cefepime (Maxipime), ampicillin-sulbactam, and piperacillin-tazobactam-may be used as single drugs to treat chorioamnionitis. (Less information is available about the effectiveness of these drugs compared to treatment with ampicillin or penicillin plus gentamicin. In addition, the toxicity profile for the baby has not been as well defined.)
In general, you receive antibiotics intravenously until you have delivered or have been without fever or other symptoms for approximately 24 hours. The antibiotics are then discontinued and you can leave the hospital. Most patients do not require oral antibiotics on an outpatient basis.
Chorioamnionitis may prolong labor and make cesarean delivery necessary. About 75% of women who are infected at term require the drug oxytocin to stimulate uterine contractions. Thirty to forty percent require cesarean delivery, usually for failure to progress in labor. While more than one-half of women with chorioamnionitis do not require cesarean, your doctor monitors you closely during labor to make sure that your uterus is contracting properly.
Your baby also requires special attention. Fetal heart rate abnormalities, such as tachycardia (fetal heart rate greater than 160 bpm), occur in over three-fourths of cases. Therefore, your baby's heart rate is monitored. Other tests may also be necessary. One such test involves determining the acid-base balance of the baby's scalp blood, which determines whether the baby is getting enough oxygen during labor.
The long-term prognosis for mothers with chorioamnionitis is excellent and future fertility is rarely compromised. The prognosis for infants delivered to infected mothers is also very good. However, some babies, particularly those who are preterm, may suffer long-term complications (such as chronic lung disease or neurologic impairment).
Because chorioamnionitis is a serious condition with a high risk of complications in the mother and her baby, your obstetrician makes every effort to prevent this infection from developing in the first place. This is done in several ways, including:
- If you are at increased risk for preterm delivery, you are screened for bacterial vaginosis in your late-second trimester. If you test positive, you should be treated as outlined above.
- All women should be screened for group B streptococcal infection at 35 to 37 weeks' gestation. If you test positive, you are treated during labor with antibiotics to reduce the risk of maternal and neonatal infection.
- Once you are in labor, your membranes should not be ruptured unless there is a compelling reason to do so. The number of vaginal examinations during labor is minimized, particularly in the early (latent) labor. Internal monitoring is used only for specific reasons-such as when the strength of uterine contractions needs to be evaluated while administering oxytocin.