What is Chorioamnionitis?
Chorioamnionitis is a clinical syndrome characterized by intrauterine infection and/or inflammation of the fetal membranes (chorion and amnion), amniotic fluid, and placenta, typically diagnosed during labor based on maternal fever combined with other signs of maternal or fetal inflammation. 1
Clinical Definition and Diagnosis
The diagnosis is usually made clinically based on maternal fever (which may be low-grade) plus at least two of the following signs: 1
- Maternal tachycardia
- Fetal tachycardia
- Uterine tenderness
- Foul-smelling or purulent amniotic fluid
- Maternal leukocytosis
In practice, maternal fever alone during labor may trigger antibiotic treatment, particularly when significant risk factors are present (prolonged labor or prolonged rupture of membranes), as a strategy to prevent neonatal infections 1.
Pathophysiology and Microbiology
Chorioamnionitis most commonly results from ascending infection from the vagina and cervix into the intrauterine cavity 2. The condition reflects either true intraamniotic infection, sterile intraamniotic inflammation, or systemic maternal inflammation (such as from epidural analgesia) 3.
The most common causative organisms are:
- Ureaplasma species (most frequent)
- Mycoplasma hominis
- Gardnerella vaginalis
- Gram-negative anaerobes (Bacteroides, Prevotella)
- Streptococcal species
Polymicrobial infections occur in approximately 70% of cases 3, 2. The likelihood of microbial invasion correlates directly with labor status and membrane rupture—organisms are found in only 1% of elective cesarean deliveries without labor, but in approximately 70% of cases with clinical chorioamnionitis 4.
Clinical Significance and Outcomes
Chorioamnionitis is an important risk factor for early-onset neonatal sepsis, particularly in women with Group B Streptococcus colonization, and can reflect intrauterine onset of infection in the neonate 1. However, the actual fetal attack rate is relatively low, with positive neonatal blood cultures ranging between 0.2% and 4% 3.
Maternal Complications:
- Postpartum endometritis
- Maternal sepsis (can occur in up to 6.8% of cases with preterm PPROM) 5
- Decreased uterine activity and failure to progress in labor
- Postpartum hemorrhage
- Prolonged hospitalization
Neonatal Complications:
- Early-onset neonatal sepsis
- Increased risk of cerebral palsy and long-term neurological disability
- Prematurity-related complications (when chorioamnionitis triggers preterm birth)
Important Clinical Pitfalls
Epidural analgesia is associated with maternal fever, which can lead to overdiagnosis of chorioamnionitis 1. However, surveillance data shows that while epidural use is common (67% of births), intrapartum fever ≥100.4°F occurs in only 3.3% of births, and physician diagnoses of chorioamnionitis remain relatively rare at 3.1% 1. Consultation with obstetric providers is essential to determine whether true chorioamnionitis is suspected 1.
Management Principles
Intrapartum antibiotic treatment can prevent neonatal sepsis and is the standard of care once chorioamnionitis is diagnosed 1. Professional societies have traditionally recommended ampicillin and gentamicin, though given the predominance of Ureaplasma species, consideration should be given to agents effective against these organisms such as azithromycin or clarithromycin 3.
All well-appearing newborns born to mothers with clinically diagnosed chorioamnionitis should undergo limited evaluation (CBC with differential and blood culture) before initiating empirical antimicrobial therapy 6. The sensitivity of CBC improves when obtained 6-12 hours after birth 6.
Chorioamnionitis by itself is not an indication for cesarean delivery, though it is associated with labor abnormalities 3. Oxytocin is often needed for labor augmentation, and uterotonic agents should be readily available for postpartum hemorrhage management 3.