Contributor: Shelley Chapman, MD Date: August 2021
Intra-amniotic infection (IAI) or chorioamnionitis is a term used to describe infection or inflammation of the amniotic fluid, membranes, fetus, placenta and/or uterus. A more precise term might be “intrauterine inflammation or infection” or Triple I. Regardless of nomenclature, the incidence of this condition varies by gestational age complicating from 0.5-10.5% of all deliveries. Obstetric risk factors include low parity, multiple digital exams, use of internal uterine/fetal monitors, meconium-stained amniotic fluid, prolonged rupture of the membranes, and the presence of certain genital tract pathogens. Maternal morbidity from intra-amniotic infection may include dysfunctional labor, postpartum uterine atony with hemorrhage, endometritis, peritonitis, sepsis, adult respiratory distress syndrome, and rarely death. IAI is associated with acute neonatal morbidity including pneumonia, meningitis, sepsis, and death, as well as long-term infant complications such as bronchopulmonary dysplasia and cerebral palsy.
The pathogenesis is most commonly an ascending infection and includes polymicrobial organisms found in the vaginal flora. These organisms include gram-negative and gram-positive (especially group B strep), aerobic and anaerobic organisms (especially Bacteroides and Peptostreptococcus).
For practical purposes intra-amniotic infection is diagnosed by clinical suspicion. Confirmed intrauterine amniotic infection is based on a positive amniotic fluid test result (bacteria or leukocytes on gram stain, low glucose concentration less than 15 mg/dL, presence of leukocyte esterase, positive culture) or histologic placental pathology. Our department has chosen to diagnose IAI as:
Maternal temperature > 102.2 degrees F in the absence of other source of infection
Single maternal temperature > 100.4 to 102.1 degrees F with any additional clinical risk factor (maternal leukocytosis > 15,000 cell/cubic mm, fetal tachycardia >160 bpm or purulent cervical drainage)
Differential diagnosis includes epidural fever, viral illness, pyelonephritis, cholecystitis, appendicitis, and other febrile morbidities. Subclinical infection can be assessed by amniocentesis for amniotic fluid testing.
Of note, in women in which GBS screening results are not available intrapartum, antibiotic prophylaxis should be given (Penicillin) if GA < 37 weeks and ROM > 18 hours or maternal temperature of > 100.4 degrees F.
Once the diagnosis of IAI is made clinically, intrapartum initiation of broad-spectrum antibiotics reduces maternal and neonatal febrile morbidity. The standard treatment of ampicillin and gentamicin is both safe and effective.
Dosing: Ampicillin 2 grams IV every 6 hours and Gentamicin 2 mg/kg IV loading dose followed by 1.5 mg/kg every 8 hours OR Gentamicin 5 mg/kg IV every 24 hours.
If a patient has a mild penicillin allergy, Cefazolin 2 grams IV every 8 hours may be substituted for Ampicillin. If a patient has a severe penicillin allergy, Clindamycin 900 mg IV every 8 hours or Vancomycin 1 gram IV every 12 hours may be substituted for Ampicillin.
Acetaminophen should be used to reduce hyperthermic stress especially in the face of fetal tachycardia. Continuous fetal heart rate monitoring should be maintained.
Term patients with IAI experience an increased frequency of dysfunctional labor. The need for oxytocin augmentation is greater as is the frequency of cesarean delivery. The adequate progression of labor should be monitored closely.
Patients treated for IAI intrapartum should receive one dose of postpartum antibiotics (Ampicillin and Gentamicin) if they deliver vaginally. Antibiotics may then be discontinued unless there are other clinical concerns. For patients who undergo cesarean delivery, Clindamycin 900 mg IV or Metronidazole 500 mg IV should be given within 60 minutes of incision as well as one additional dose of Ampicillin and Gentamicin. No other “antibiotic prophylaxis” is needed; however, if the patient has a BMI > 30 or has had prolonged ROM ( > 18 hours ), continuing Ampicillin, Gentamycin and Clindamycin until afebrile at least 24 hours is recommended.
Treatment failures will be defined as a patient with a single temperature after the postpartum dose of antibiotics of >102.2 degrees F or two temperatures >100.4 degrees F at least four hours apart. Patients identified as treatment failures should be evaluated by physical exam. Patients identified as treatment failures should immediately receive Ampicillin 2 g IV every 6 hours, Gentamicin 7 mg/kg ideal body weight IV every 24 hours and Clindamycin 900 mg IV every 8 hours (Metronidazole 500 mg IV every 12 hours may be substituted for Clindamycin). If the patient is allergic to Penicillin, Cefazolin or Vancomycin should be substituted for Ampicillin. This regimen should be continued until the woman has been afebrile and asymptomatic for at least 24 hours. Blood cultures and other diagnostic test are performed only as deemed clinically indicated by the treating physician.
The patient record should clearly state the basis for diagnosing intra-amniotic infection, GA, maternal GBS status, the duration of rupture of membranes and labor, maternal course including epidural or prostaglandin use, and any pertinent laboratory results. Umbilical cord blood gas should be sent on a patient with a diagnosis of IAI. The placenta of the patient with the diagnosis of IAI should be sent for histopathology.
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