What is the cause and treatment of chorioamnionitis?

Causes and Treatment of Chorioamnionitis

Causes of Chorioamnionitis

Chorioamnionitis is primarily caused by ascending polymicrobial infection from the lower genital tract, with Ureaplasma species being the most common pathogen, followed by Mycoplasma hominis and Gram-negative anaerobes. 1, 2

Microbiology

• Polymicrobial infections occur in approximately 70% of cases 1
• Most frequently isolated organisms include:
  • Ureaplasma urealyticum (most common) 1, 2
  • Mycoplasma hominis 2
  • Gram-negative anaerobes 2
  • Group B Streptococcus 3
  • Escherichia coli 3

Pathogenesis

• Ascending infection from the vagina and cervix is the primary route 2
• Commonly associated with premature rupture of membranes 2
• Can also result from sterile intraamniotic inflammation (inflammation without bacteria) or systemic maternal inflammation induced by epidural analgesia 1

Treatment of Chorioamnionitis

Intrapartum Antibiotic Therapy

The first-line treatment is intravenous ampicillin 2g every 6 hours combined with gentamicin 1.5 mg/kg every 8 hours, initiated immediately upon diagnosis during the intrapartum period. 4, 5

Standard Regimen

• Ampicillin 2g IV every 6 hours PLUS gentamicin 1.5 mg/kg IV every 8 hours 4, 5
• Antibiotics should be started intrapartum, not delayed until after delivery 4
• If cesarean delivery is performed, add clindamycin 900mg IV at umbilical cord clamping 4, 5

Alternative Regimens for Penicillin Allergy

• For patients without history of anaphylaxis, angioedema, respiratory distress, or urticaria: cefazolin is the preferred agent 6
• For patients with history of severe allergic reactions: clindamycin or vancomycin should be used 6

Postpartum Antibiotic Duration

After vaginal delivery, only one additional scheduled dose of antibiotics postpartum is sufficient for immune-competent women. 5

• High-quality randomized trial demonstrated no difference in treatment failure between single additional dose (4.6%) versus extended therapy until afebrile for 24 hours (3.5%) 5
• After cesarean delivery with clindamycin added: continue only until the next scheduled dose 5
• Extended postpartum antibiotics are not necessary after either vaginal or cesarean delivery 4

Emerging Evidence for Enhanced Coverage

Given the predominance of Ureaplasma species, consideration should be given to antimicrobial agents effective against these organisms, such as azithromycin or clarithromycin. 1

• A promising regimen includes ceftriaxone, clarithromycin, and metronidazole, which provides coverage against the most commonly identified microorganisms and has been shown to eradicate intraamniotic infection 4, 1
• This broader coverage addresses the polymicrobial nature and includes atypical organisms frequently missed by standard therapy 1

Additional Management Considerations

Delivery Timing

• Once chorioamnionitis is diagnosed, delivery should be considered regardless of gestational age 4
• Vaginal delivery is the safer option; cesarean delivery should be reserved for standard obstetrical indications 4
• Delivery should not be delayed to complete corticosteroids or magnesium sulfate 4

Labor Management

• Patients may require higher doses of oxytocin to achieve adequate uterine activity 4
• Chorioamnionitis is associated with decreased uterine activity, failure to progress, and postpartum hemorrhage 1
• Have uterotonic agents readily available for postpartum hemorrhage management 1

Antipyretic Therapy

• Acetaminophen can be administered, though clear evidence of benefit is lacking 4

Neonatal Management

All well-appearing newborns whose mothers had suspected chorioamnionitis should undergo a limited evaluation (blood culture and CBC with differential and platelet count) and receive antibiotic therapy pending culture results. 3, 6, 7

• Neonatal antibiotic therapy should include intravenous ampicillin for GBS plus coverage for other organisms including E. coli and gram-negative pathogens 3
• The sensitivity of CBC is improved if delayed 6-12 hours after birth 3, 6
• Consultation with obstetric providers is important to determine the level of clinical suspicion, as some signs are nonspecific 3, 6

Common Pitfalls

• Do not delay antibiotic administration until after delivery—intrapartum treatment is essential 4
• Do not continue prolonged postpartum antibiotics—one additional dose is sufficient for most patients 5
• Do not forget clindamycin at cord clamping for cesarean deliveries—this provides anaerobic coverage 4, 5
• Consider that standard ampicillin-gentamicin may not adequately cover Ureaplasma species, which are the most common causative organisms 1