Chorioamnionitis is a serious bacterial infection that develops during pregnancy, typically affecting the tissues surrounding the fetus. This condition involves inflammation or infection of the membranes and amniotic fluid that enclose the baby. Although it can lead to complications for both the mother and the developing infant, early recognition and prompt medical management significantly improve outcomes. It affects an estimated one to six percent of term gestations.
Defining Chorioamnionitis
Chorioamnionitis, also called intra-amniotic infection, involves acute inflammation of the fetal membranes and the placenta. The name derives from the two primary membranes forming the fluid-filled sac: the outer chorion and the inner amnion. The amniotic fluid and the placenta itself can also become involved in the infectious process.
The infection most commonly follows an “ascending” pathway, where bacteria from the mother’s lower genital tract (vagina or cervix) travel upward into the uterine cavity. Common pathogens include E. coli, Group B Streptococcus (GBS), and species of Ureaplasma and Mycoplasma. These microorganisms access the normally sterile environment, causing inflammation that activates the mother’s and fetus’s inflammatory response systems.
This inflammation can promote uterine contractions and cervical changes, often leading to preterm birth. Less common pathways include hematogenous spread through the bloodstream or direct contamination during invasive procedures like amniocentesis. Diagnosis is based on clinical signs, lab results, or microscopic examination of the placenta after delivery.
Key Risk Factors
Several factors increase the likelihood of developing chorioamnionitis.
Rupture of Membranes and Labor
The premature rupture of membranes (PROM) is a significant factor, especially when the time between rupture and delivery is prolonged. Compromising the protective barrier of the amniotic sac creates a direct path for bacteria to ascend from the vagina into the uterus. Prolonged labor is also a contributing factor, as extended cervical dilation provides more opportunity for bacteria to reach the membranes, particularly when combined with ruptured membranes. Frequent vaginal examinations during labor, especially after PROM, are associated with an elevated risk due to the potential introduction of flora into the upper genital tract.
Maternal Conditions
Pre-existing maternal conditions also play a role, such as colonization with Group B Streptococcus (GBS) or the presence of other vaginal or sexually transmissible infections. Untreated GBS bacteriuria is strongly linked to the condition due to the high concentration of bacteria in the genital tract. The risk is also higher during a first pregnancy (nulliparity) and with internal monitoring of the fetus or uterus.
Recognizing Symptoms and Diagnosis
Recognizing chorioamnionitis relies primarily on clinical observation, confirmed by laboratory tests. The most consistent sign is maternal fever, typically 100.4°F (38.0°C) or higher, often accompanied by other findings indicating uterine infection.
Medical staff may observe maternal tachycardia (rapid heart rate, usually exceeding 100 beats per minute). Fetal tachycardia, defined as a baseline heart rate above 160 beats per minute for an extended period, is also a common indicator. The mother may also experience uterine tenderness or pain upon abdominal palpation.
Diagnosis is confirmed when maternal fever is present alongside one or more of the following: fetal tachycardia, purulent or foul-smelling amniotic fluid or vaginal discharge, or an elevated white blood cell count. A total blood leukocyte count exceeding 15,000 cells/μL supports the diagnosis. Although amniotic fluid analysis can confirm bacteria, the diagnosis is usually made using clinical and laboratory criteria to allow for urgent treatment.
Treatment Protocols
Once chorioamnionitis is diagnosed, immediate treatment is initiated to control the infection and prevent complications. The primary protocol involves administering broad-spectrum intravenous antibiotics. The standard regimen typically combines antibiotics, such as ampicillin and gentamicin, to cover the most likely bacterial pathogens.
Antibiotic therapy begins immediately, even before delivery, to reduce the bacterial load in the amniotic fluid and maternal bloodstream. This aims to resolve the mother’s infection and reduce the risk of the baby developing an infection. If a cesarean delivery is performed, an additional antibiotic, such as clindamycin or metronidazole, is often added to cover anaerobic bacteria and reduce the risk of postpartum uterine infection.
Delivery of the fetus and placenta is necessary to fully resolve the infection, regardless of gestational age. The source of the infection (placenta and membranes) must be removed to prevent recurrence and systemic spread. After delivery, the mother continues to receive intravenous antibiotics until the infection resolves.
Potential Health Implications
Chorioamnionitis can result in serious health consequences for both the mother and the newborn.
Maternal Complications
Potential complications for the mother include postpartum hemorrhage due to impaired uterine contractility. The infection can also lead to maternal sepsis, a life-threatening systemic response, or endometritis (infection of the uterine lining after birth). Mothers have an increased chance of requiring a cesarean delivery, which carries higher risks of surgical wound infection or pelvic abscess formation. Though rare, severe cases can progress to disseminated intravascular coagulation (DIC) or multi-organ failure if the infection is not rapidly controlled. The long-term outlook for the mother is generally excellent once the infection is treated.
Neonatal Complications
For the infant, exposure increases the risk of premature birth, as inflammation can trigger early labor. The most immediate concern is early-onset neonatal sepsis, a potentially life-threatening bloodstream infection. Localized infections, such as pneumonia or meningitis, occur in about five to ten percent of exposed babies.
In the long term, infants who experience the inflammatory response, especially those born prematurely, have a higher risk of developing severe complications. These outcomes include respiratory distress syndrome, which requires breathing support, and long-term neurological disabilities such as cerebral palsy in severe cases. The intensity of the baby’s inflammatory reaction, known as Fetal Inflammatory Response Syndrome, is a key factor in predicting these neurodevelopmental outcomes.