creation date: 2026-01-15 18:59
tags: Pathologies
Chorioamnionitis
Background
Definitions
Chorioamnionitis refers to an infection of the uterus and its contents (chorion, amnion, or both) that occurs before labour, during labour, or after delivery. It can be acute, subacute or chronic.
Clinical chorioamnionitis is what chorioamnionitis almost always refer to. Intraamniotic infection is used interchangeably but technically refers to the infection involving the amniotic fluid, fetus, and umbilical cord in addition to the membranes.
Histological chorioamnionitis is used by pathologist to describe inflammation without typical clinical or microbiological findings.
Etiology and Risk Factors
Migration of cervicovaginal microorganisms is responsible for chorioamnionitis in the majority of cases. This typically consist of multiple species of typically enteric microorganisms. The most common are:
- Genital mycoplasmas (Ureaplasma and Mycoplasma species)
- Anaerobes (eg. Gardnerella vaginalis, Bacterioides spp.)
- Enteric gram-negative bacilli
- Group B Streptococcus
Rarely, transplacental passage of microorganism from maternal blood may cause chorioamnionitis. In such case, infection is usually monopathogenic.
- TORCH pathogens - Toxoplasmosis, Others (syphilis, HIV, varicella-zoster, parovirus B19, Zika), Rubella, Cytomegalovirus, Herpes simplex
- Listeria monocytogenes
- Plasmodium species
- Campylobacter species
Risk factors for developing chorioamnionitis generally involve longer duration of labour and ruptured membranes. Other obstetrics factors such as iatrogenic transfer of pathogens via instrument (eg. balloon catheter, fetal scalp probe).
Pathogenesis
As mentioned, migration of cervicovaginal microorganisms causes chorioamnionitis. The microorganism passes through the cervical canal to the decidual-chorionic interface which then passes into the amniotic cavity and eventually the fetus.
Microbial infection activates the maternal/fetal inflammatory systems which generally leads to labour and/or prelabour rupture of membranes.
Clinical Presentation
Signs & Symptoms
Chorioamnionitis most often occurs in pregnancies with prelabour rupture of membranes but can occur with intact membranes, especially when labouring.
Findings include:
- Fever (~100%)
- Maternal leukocytosis (WBC >15,000; 80%)
- Maternal tachycardia (65%)
- Fetal tachycardia (55%)
- Uterine tenderness (15%)
- Bacteremia (10%)
- Purulent or malodorous amniotic fluid
Subclinical cases may be asymptomatic
History & Physical Exam
Physical should include speculum exam to visualize cervix.
Diagnosis
Criteria
Chorioamnionitis is a clinical diagnosis, with the key criterion being maternal fever without another identifiable source.
Presumptive diagnosis
A presumptive diagnosis can be made in a pregnant patient with fever ≥39C once or 38-38.9C on ≥2 measurement 30 minutes apart wihtout another clear source plus one of the following:
- Baseline fetal heart rate >160 bpm for ≥10 mins excluding accelerations, decelerations, and periods of marked variability
- Maternal WBC >15,000 in absence of corticosteroids (and ideally with left shift)
- Purulent-appearing fluid from cervical os during speculum exam
Confirmed diagnosis
Confirmation is made if a presumptive diagnosis has one or more of the following laboratory findings from amniotic fluid obtained from amniocentesis:
- Positive gram stain of amniotic fluid
- Low glucose level in amniotic fluid
- Postive amniotic fluid culture
- High WBC count (>30) in amniotic fluid in absence of a bloody tap
- Histopathologic evidence of infection and/or inflammation in the placenta, fetal membrane, or the umbilical cord vessels
Work-up
Initial evaluation should have:
- CBC
- Diagnostic testing for other possible infection if another cause suspected
Amniocentesis is obtained if the presumptive diagnosis is uncertain and an alternative diagnosis is suspected.
- Gram stain
- Glucose concentration
- WBC count
- Leukocyte esterase activity
Sepsis should be suspected and serum lactate should be ordered in patients who meet the maternal early warning criteria (MEWC):
- SBP <90 or >160
- DBP >100
- HR <50 or >120
- RR <10 or >30
- O2 sat on room air <95%
- Oliguria <35 mL/hr for ≥2 hrs
- Maternal agitation, confusion, or unresponsiveness
- Headache or SOB in preeclampsia patient
Differential
The differential can be broad owing to the nonspecific clinical findings.
Labour
Normal labour may involve fever. This may be due to:
- Dehydration
- Use of prostaglandins for cervical ripening
- Neuraxial anesthesia (challenging as anesthesia also masks uterine tenderness)
Placental abruption
- Can causes uterine tenderness and tachycardia
- Usually fever is absent
Other infections
Extrauterine infections can cause fever:
- Pyelonephritis
- Influenza
- Pneumonia
Red Flags / Complications
Sequelae of chorioamnionitis are increased risk of:
- Preterm birth (whether through spontaneous preterm labour, PPROM, PROM, or medically indicated preterm birth)
- Dysfunctional labour (protraction, arrest disorders, and increased risk of c-section)
- Sepsis
- Postpartum infection
Management
Initial Treatment
Antibiotic therapy is given prompted following diagnosis. For labouring patients, this is generally a broad-spectrum parenteral option that covers common cervicovaginal pathogens:
- Ampicillin 2g IV q6h AND
- Gentamicin 5 mg/kg IV once daily
For patients who will undergo cesarean birth, anaerobic coverage is added to the above:
- Metronidazole 500 mg IV OR
- Clindamycin 900 mg IV q8h
For patients with penicillin allergy, vancomycin can replace ampicillin but this may be institution dependent.
Antenatal corticosteroids should not delay delivery. The evidence is unclear but two conflicting options are:
- Avoid corticosteroids as immunosuppressive effects may worsen outcomes
- Administer corticosteroids as exposure may have beneficial effects and harm is not established in patients with adequate antibiotic therapy
Delivery
During delivery:
- Continuous electronic fetal monitoring
- Acetaminophen as antipyretic
Following delivery: antibiotics are:
- Discontinued if vaginal birth
- Continued until patient has been afebrile and asymptomatic for at least 24-48 hours