Diagnostic Criteria for Chorioamnionitis
Chorioamnionitis should be diagnosed clinically based on maternal fever (≥100.4°F/38.0°C) plus at least one additional clinical finding: maternal tachycardia, fetal tachycardia, uterine tenderness, foul-smelling amniotic fluid, or maternal leukocytosis. 1
Clinical Diagnostic Framework
The Centers for Disease Control and Prevention (CDC) provides the standard diagnostic approach that requires:
Primary Criterion (Required)
- Maternal fever ≥100.4°F (38.0°C) 1
Secondary Criteria (At Least One Required)
- Maternal tachycardia 1
- Fetal tachycardia 1
- Uterine tenderness 1
- Foul-smelling amniotic fluid 1
- Maternal leukocytosis 1
Important Limitations and Caveats
These clinical criteria have significant diagnostic limitations. The accuracy of individual clinical signs for identifying true intra-amniotic infection ranges only between 46.7% and 57.8%, and even combining fever with three or more clinical criteria does not substantially improve diagnostic accuracy 2. Only approximately 54% of patients diagnosed with clinical chorioamnionitis at term actually have bacteria in the amniotic fluid with evidence of intra-amniotic inflammation 2.
Performance of Individual Signs
- Maternal tachycardia: 51.1% accuracy 3
- Fetal tachycardia: 57.8% accuracy 3
- Maternal leukocytosis: 55.6% accuracy 3
Alternative Diagnostic Approach
A newer objective scoring system may offer improved diagnostic accuracy (AUC 0.741 vs 0.621 for traditional criteria), using only objective indicators 4:
- Body temperature ≥38.5°C: 2 points 4
- C-reactive protein ≥1.0 mg/dL: 2 points 4
- White blood cell count ≥12 × 10⁹/L: 1 point 4
- Nulliparity: 1 point 4
- Diagnosis threshold: ≥4 points 4
Critical Management Implications
Do not withhold antibiotics pending amniocentesis results or wait for maternal fever to develop in suspected chorioamnionitis 1. Antibiotics should be initiated within 3 hours of fever recognition, or within 1 hour if septic shock is suspected 1.
Common Pitfall
The clinical signs used for diagnosis are neither sensitive nor specific, yet the diagnosis requires a high index of suspicion because timely antibiotic treatment and delivery are essential to reduce maternal and neonatal infectious complications 5, 6. The subjective nature of these findings limits their clinical utility, particularly when consultation with obstetric providers is important to determine the level of clinical suspicion 7.