Intraamniotic infection: Clinical sciences

Intraamniotic infection, commonly called chorioamnionitis, is an infection that causes inflammation of the amniotic fluid, placenta, decidua, fetus, fetal membranes, or any combination of these.

It is usually caused by an ascending infection of polymicrobial bacteria, including both aerobic and anaerobic species, that are present in the vaginal flora. While both preterm and term pregnancies can be affected, it most commonly affects full term pregnancies and usually presents while patients are in labor.

Intraamniotic infection is associated with an increased risk of both maternal and neonatal complications. Maternal complications include dysfunctional labor, postpartum uterine atony leading to hemorrhage, endometritis, peritonitis, sepsis, acute respiratory distress syndrome and, in some instances, death. In neonates, acute complications include pneumonia, meningitis, sepsis, and possibly death; as well as long-term complications such as bronchopulmonary dysplasia and cerebral palsy.

When assessing a patient who presents with a chief concern suggesting an intraamniotic infection, start with a focused history and physical exam. Patients may have one or more risk factors, including low parity, exposure to multiple digital examinations, use of internal monitors like an intrauterine pressure catheter or fetal scalp electrode, meconium-stained amniotic fluid, genital tract pathogens such as group B Streptococcus or a sexually transmitted infection, prolonged rupture of membranes, defined as greater than 18 hours, and prolonged labor.

Next, evaluate your patient for intraamniotic infection. This is done by checking your patient's temperature, reviewing the fetal heart tracing, obtaining or reviewing a CBC, and performing a sterile speculum exam.

A suspected intraamniotic infection is diagnosed clinically when a patient has either a one-time fever, with a temperature of at least 39.0 degrees Celsius; or an elevated temperature between 38.0 and 38.9 degrees Celsius, along with at least one of the following clinical findings: fetal tachycardia, defined as a fetal heart rate above 160 beats per minute; maternal leukocytosis, with a white blood cell count above 15,000; or the presence of purulent fluid from the cervical os. Fundal tenderness may also be present.

Okay, here is a clinical pearl! The diagnosis of a suspected intraamniotic infection can be confirmed objectively either by amniocentesis and analysis of amniotic fluid or by placental pathology. Amniotic fluid analysis will reveal a positive Gram stain, low glucose, or a positive amniotic fluid culture; whereas placenta pathology will show histologic evidence of infection and placental inflammation. In practice, however, all patients with clinical suspicion of an intraamniotic infection need prompt intervention, so the distinction between a suspected and a confirmed intraamniotic infection is meaningful only in research settings.

First let's look at management of isolated maternal fever. Now, if your patient has an elevated temperature between 38.0 and 38.9 degrees Celsius, with or without a persistent temperature elevation 30 minutes later and with no other clinical findings indicating intraamniotic infection, you can diagnose an isolated maternal fever.

Treatment involves first ruling out other potential benign causes of a transient maternal temperature elevation such as epidural anesthesia, prostaglandin use, dehydration, hyperthyroidism, or excess ambient heat.