Acute chorioamnionitis is a serious bacterial infection that develops during pregnancy, affecting the tissues surrounding the fetus and the fluid within the womb. This condition involves the placenta, the membranes, and the amniotic fluid, representing a potentially life-threatening complication for both the pregnant patient and the baby. This infection is a common cause of fever in the peripartum period and is associated with a significant portion of preterm births in the United States.
What Acute Chorioamnionitis Is
Acute chorioamnionitis describes an inflammation or infection of the membranes that enclose the fetus, specifically the chorion (the outer membrane) and the amnion (the inner membrane). The term is sometimes referred to as Intra-amniotic Infection (IAI) or Triple I (Intrauterine Infection or Inflammation).
The mechanism of infection is typically an ascending process, meaning bacteria travel upward from the lower genital tract, such as the vagina and cervix, into the uterus. These bacteria, often polymicrobial, colonize the lower pole of the uterus and gain entry, especially after the protective seal of the cervix is compromised. Common causative organisms include E. coli and Group B Streptococcus (GBS).
In some instances, the infection can occur with intact membranes, although it is most frequently associated with rupture of the amniotic sac. The inflammation can be diagnosed histologically by examining the placenta after delivery, or clinically based on the patient’s physical signs.
Factors That Increase Risk
Several predisposing conditions increase a pregnant patient’s vulnerability to developing acute chorioamnionitis. One primary factor is prolonged rupture of membranes, which occurs when the amniotic sac breaks long before labor and delivery. This loss of the protective barrier provides a direct pathway for ascending bacteria.
Another established risk factor is a high number of vaginal examinations performed after the membranes have ruptured, as each examination can potentially introduce bacteria closer to the membranes. Similarly, the use of internal monitoring devices during labor, such as an intrauterine pressure catheter or a fetal scalp electrode, can also breach the protective barrier.
The presence of certain bacteria in the lower genital tract, such as colonization with Group B Streptococcus, is also a factor. Other infections like bacterial vaginosis or sexually transmitted infections can disrupt the normal vaginal flora. Additionally, preterm labor and a long duration of labor are associated with a higher incidence of this condition.
Identifying and Treating the Infection
The diagnosis of acute chorioamnionitis is primarily based on a combination of clinical signs and symptoms. The most defining sign is the presence of maternal fever, typically 100.4°F (38.0°C) or higher, which warrants immediate investigation for intra-amniotic infection.
Fever is often accompanied by signs of a systemic inflammatory response, including maternal tachycardia (a rapid heart rate) and fetal tachycardia (a sustained baseline fetal heart rate greater than 160 beats per minute). The patient may also experience uterine tenderness or notice foul-smelling amniotic fluid or vaginal discharge. Laboratory findings, such as an elevated maternal white blood cell count, also support the diagnosis.
Treatment is time-sensitive and requires a dual approach. The first is the immediate administration of broad-spectrum intravenous antibiotics, chosen to cover likely causative bacteria like E. coli and GBS. The second is delivery of the fetus, regardless of gestational age, as this removes the source of the infection. Antibiotic administration must continue until after delivery is complete and the patient’s condition has improved.
Impact on Mother and Baby
If acute chorioamnionitis is not diagnosed and treated rapidly, the infection can progress to cause significant problems for the patient. One serious potential outcome is maternal sepsis, a life-threatening systemic response to the infection. The inflammation can also interfere with the uterus’s ability to contract effectively after delivery, increasing the risk of postpartum hemorrhage.
Infections of the uterine lining, known as endometritis, are a common complication following delivery. The presence of the infection also significantly increases the likelihood that a patient will require a cesarean delivery. In the most severe instances, the infection can lead to septic shock or a need for a hysterectomy.
The baby also faces serious consequences from exposure to the infection and inflammatory mediators. The most immediate concern is neonatal sepsis, a bloodstream infection in the newborn. Other severe infections in the newborn can include pneumonia and meningitis.
Infants, particularly those born prematurely due to the infection, are also at increased risk for long-term neurological complications. Exposure to the intrauterine inflammation is associated with an increased likelihood of developing conditions such as cerebral palsy and other neurodevelopmental disabilities.