Korioamnionitis
Published on May 16, 2026
Risk Factors
Prolonged rupture of membranes (>18 hours), multiple digital vaginal exams, preterm labor, nulliparity, prolonged labor, Group B Streptococcus (GBS) colonization, bacterial vaginosis, internal fetal monitoring, cervical cerclage, meconium-stained amniotic fluid
Etiology
Ascending polymicrobial infection from the lower genital tract through the cervix into the amniotic cavity; most common organisms include Ureaplasma urealyticum, Mycoplasma hominis, Gardnerella vaginalis, E. coli, GBS, and anaerobes
Presentation
Pregnant woman (usually intrapartum) with fever, uterine tenderness, foul-smelling amniotic fluid
Classic Exam
Maternal fever (>38.0 C / 100.4 F), uterine fundal tenderness, maternal tachycardia (>100 bpm), fetal tachycardia (>160 bpm), purulent or foul-smelling amniotic fluid
Diagnostics
Clinical diagnosis based on maternal intrapartum fever plus supporting criteria; maternal leukocytosis (>15,000/microL, though nonspecific in labor); amniotic fluid Gram stain and culture (gold standard but rarely needed before treatment)
Management
Immediate intrapartum IV antibiotics (ampicillin + gentamicin) and delivery (do not delay for antibiotics to take effect); cesarean section only for standard obstetric indications, not for chorioamnionitis itself
Keywords
"Intrapartum fever," "prolonged rupture of membranes," "uterine tenderness," "fetal tachycardia," "foul-smelling fluid"
01Pathophysiology
Chorioamnionitis is an intraamniotic infection involving inflammation of the chorion and amnion, the membranes surrounding the fetus and amniotic fluid. The dominant route of infection is ascending, meaning bacteria from the vaginal and cervical flora migrate upward through the cervical os into the uterine cavity. This is why prolonged rupture of membranes is the single strongest risk factor: once the membrane barrier is breached, bacteria gain direct access to the amniotic space.
Once inside the amniotic cavity, bacteria trigger a robust maternal and fetal inflammatory response. Cytokines such as IL-6 and TNF-alpha are released, causing vasodilation and increased vascular permeability in the uterine wall. This explains the uterine tenderness and maternal fever. The maternal cardiovascular system responds to systemic inflammation and fever with tachycardia.
Fetal tachycardia (baseline heart rate >160 bpm) occurs because the fetus is exposed to the same inflammatory milieu. The infected amniotic fluid is in direct contact with fetal skin, lungs (via fetal breathing movements), and the gastrointestinal tract (via swallowing). This fetal exposure can lead to fetal inflammatory response syndrome (FIRS), which is associated with neonatal complications such as early-onset sepsis, pneumonia, and long-term risks including cerebral palsy and bronchopulmonary dysplasia.
The infection is almost always polymicrobial, reflecting the mixed flora of the lower genital tract. This is why broad-spectrum antibiotic coverage is required rather than a narrow-spectrum agent.
02Classification and Clinical Manifestation
The current classification system (sometimes referred to as the "Triple I" framework) stratifies intraamniotic inflammation and infection into three tiers:
Isolated maternal fever
Definition
Single maternal temperature of 39.0 C (102.2 F) or greater, OR a temperature of 38.0 to 38.9 C that persists on repeat measurement 30 minutes later
Clinical Features
Fever alone without additional clinical signs; may be due to epidural analgesia or other non-infectious causes
Suspected intraamniotic infection
Definition
Maternal intrapartum fever (as above) PLUS one or more of the following: fetal tachycardia (>160 bpm), maternal leukocytosis (>15,000/microL), purulent cervical drainage
Clinical Features
Clinical picture consistent with infection but without definitive microbiologic proof
Confirmed intraamniotic infection
Definition
Positive amniotic fluid testing: Gram stain showing bacteria or leukocytes, low amniotic fluid glucose (<14 mg/dL), positive culture, or high IL-6 levels in amniotic fluid
Clinical Features
Rarely obtained before delivery; amniocentesis is performed only in ambiguous preterm cases where the decision to deliver versus expectant management hinges on confirming infection
Category | Definition | Clinical Features |
|---|---|---|
Isolated maternal fever | Single maternal temperature of 39.0 C (102.2 F) or greater, OR a temperature of 38.0 to 38.9 C that persists on repeat measurement 30 minutes later | Fever alone without additional clinical signs; may be due to epidural analgesia or other non-infectious causes |
Suspected intraamniotic infection | Maternal intrapartum fever (as above) PLUS one or more of the following: fetal tachycardia (>160 bpm), maternal leukocytosis (>15,000/microL), purulent cervical drainage | Clinical picture consistent with infection but without definitive microbiologic proof |
Confirmed intraamniotic infection | Positive amniotic fluid testing: Gram stain showing bacteria or leukocytes, low amniotic fluid glucose (<14 mg/dL), positive culture, or high IL-6 levels in amniotic fluid | Rarely obtained before delivery; amniocentesis is performed only in ambiguous preterm cases where the decision to deliver versus expectant management hinges on confirming infection |
This classification matters on exams because isolated maternal fever alone does not automatically equal chorioamnionitis. The vignette must include at least one additional clinical sign to move from "isolated fever" to "suspected intraamniotic infection." Epidural analgesia is a well-known cause of isolated intrapartum fever that can mimic chorioamnionitis.
03Diagnostic Workup
Clinical criteria
Role
Best initial "test"
Key Findings
Maternal intrapartum fever plus at least one: fetal tachycardia, maternal tachycardia, uterine tenderness, purulent/foul-smelling amniotic fluid
CBC with differential
Role
Supportive
Key Findings
WBC >15,000/microL (note: mild leukocytosis is physiologic in labor, so this is nonspecific in isolation)
Blood cultures
Role
Obtained if sepsis is suspected
Key Findings
Not required for diagnosis; drawn before antibiotics when clinical picture suggests bacteremia
Amniotic fluid analysis (Gram stain, culture, glucose, IL-6)
Role
Gold standard / most accurate
Key Findings
Positive Gram stain, positive culture, glucose <14 mg/dL; rarely performed clinically before initiating treatment
Placental pathology
Role
Retrospective confirmation
Key Findings
Neutrophilic infiltration of the chorion and amnion on histopathology (definitively confirms the diagnosis postpartum)
Test | Role | Key Findings |
|---|---|---|
Clinical criteria | Best initial "test" | Maternal intrapartum fever plus at least one: fetal tachycardia, maternal tachycardia, uterine tenderness, purulent/foul-smelling amniotic fluid |
CBC with differential | Supportive | WBC >15,000/microL (note: mild leukocytosis is physiologic in labor, so this is nonspecific in isolation) |
Blood cultures | Obtained if sepsis is suspected | Not required for diagnosis; drawn before antibiotics when clinical picture suggests bacteremia |
Amniotic fluid analysis (Gram stain, culture, glucose, IL-6) | Gold standard / most accurate | Positive Gram stain, positive culture, glucose <14 mg/dL; rarely performed clinically before initiating treatment |
Placental pathology | Retrospective confirmation | Neutrophilic infiltration of the chorion and amnion on histopathology (definitively confirms the diagnosis postpartum) |
Chorioamnionitis is primarily a clinical diagnosis. In a laboring patient at term with intrapartum fever plus fetal tachycardia and uterine tenderness, you do not need to wait for lab results before initiating treatment. The exam tests this principle: when the clinical picture is clear, the next best step is antibiotics and delivery, not amniocentesis.
Amniocentesis for amniotic fluid analysis is reserved for the preterm patient with preterm premature rupture of membranes (PPROM) where the clinical picture is ambiguous. In this scenario, confirming or excluding intraamniotic infection determines whether the fetus should be delivered immediately or managed expectantly with corticosteroids for lung maturity. This is a commonly tested decision point.
Leukocytosis must be interpreted carefully. Labor itself, corticosteroid administration, and even normal pregnancy can elevate the WBC count, so an isolated elevated WBC does not confirm the diagnosis. A leftward shift (bandemia) is more suggestive but still not diagnostic on its own.
04Management and Treatment
Intrapartum (acute)
Intervention
IV Ampicillin + IV Gentamicin
Details
Ampicillin 2 g IV every 6 hours + Gentamicin 5 mg/kg IV every 24 hours (or traditional dosing: 1.5 mg/kg every 8 hours); start immediately upon diagnosis
Cesarean delivery
Intervention
Add anaerobic coverage
Details
Add Clindamycin 900 mg IV every 8 hours OR Metronidazole 500 mg IV every 8 hours for enhanced anaerobic coverage of surgical wound flora
Delivery
Intervention
Expedite but do not mandate cesarean
Details
Delivery should proceed without delay; chorioamnionitis alone is not an indication for cesarean section; vaginal delivery is preferred if otherwise appropriate
Postpartum
Intervention
Continue or stop antibiotics based on delivery route
Details
After vaginal delivery: one additional dose of antibiotics postpartum is generally sufficient, and many institutions discontinue antibiotics entirely if the patient is afebrile. After cesarean delivery: continue antibiotics until the patient is afebrile and clinically improved for at least 24 hours
GBS prophylaxis
Intervention
Ampicillin in the chorioamnionitis regimen covers GBS
Details
No separate GBS prophylaxis is needed when the patient is already receiving ampicillin-based chorioamnionitis treatment
Setting | Intervention | Details |
|---|---|---|
Intrapartum (acute) | IV Ampicillin + IV Gentamicin | Ampicillin 2 g IV every 6 hours + Gentamicin 5 mg/kg IV every 24 hours (or traditional dosing: 1.5 mg/kg every 8 hours); start immediately upon diagnosis |
Cesarean delivery | Add anaerobic coverage | Add Clindamycin 900 mg IV every 8 hours OR Metronidazole 500 mg IV every 8 hours for enhanced anaerobic coverage of surgical wound flora |
Delivery | Expedite but do not mandate cesarean | Delivery should proceed without delay; chorioamnionitis alone is not an indication for cesarean section; vaginal delivery is preferred if otherwise appropriate |
Postpartum | Continue or stop antibiotics based on delivery route | After vaginal delivery: one additional dose of antibiotics postpartum is generally sufficient, and many institutions discontinue antibiotics entirely if the patient is afebrile. After cesarean delivery: continue antibiotics until the patient is afebrile and clinically improved for at least 24 hours |
GBS prophylaxis | Ampicillin in the chorioamnionitis regimen covers GBS | No separate GBS prophylaxis is needed when the patient is already receiving ampicillin-based chorioamnionitis treatment |
The single most important management principle is: do not delay delivery to "complete a course" of antibiotics. Once chorioamnionitis is diagnosed, the source of infection is the intrauterine environment, and the definitive treatment is delivery. Antibiotics are adjunctive and should be started promptly to reduce neonatal and maternal morbidity, but they do not replace the need for delivery.
For patients with a penicillin allergy, Vancomycin (1 g IV every 12 hours) replaces ampicillin. Gentamicin is retained for gram-negative coverage.
Oxytocin augmentation should be used as needed to achieve vaginal delivery. If labor progress stalls, standard labor management algorithms apply. Cesarean section is performed only for obstetric indications such as non-reassuring fetal heart tracing, arrest of labor, or malpresentation. Chorioamnionitis actually increases the risk of cesarean section (due to dysfunctional labor), but this is a consequence, not an indication.
A commonly tested nuance: fever that develops after epidural placement can be confused with chorioamnionitis. Epidural-related fever is typically low-grade, not associated with fetal tachycardia or uterine tenderness, and develops gradually over several hours. When the vignette includes only isolated fever after epidural placement without other signs, the answer is observation rather than antibiotics.
05Differential Diagnosis and Distractors
Epidural-related fever
Why It Looks Similar
Intrapartum fever after epidural placement
Key Discriminator
Isolated low-grade fever without fetal tachycardia, uterine tenderness, or foul-smelling fluid; fever onset correlates with epidural timing; no supporting lab or clinical signs of infection
Urinary tract infection / Pyelonephritis
Why It Looks Similar
Fever in pregnancy, leukocytosis
Key Discriminator
Flank pain and costovertebral angle tenderness; positive urinalysis with pyuria and bacteriuria; no uterine tenderness or fetal tachycardia; often occurs antepartum rather than intrapartum
Endometritis
Why It Looks Similar
Uterine tenderness, fever, polymicrobial etiology
Key Discriminator
Occurs postpartum, not intrapartum; follows delivery (particularly cesarean); uterine tenderness with lochia that may be foul-smelling; the timing distinction is the key discriminator
Placental abruption
Why It Looks Similar
Uterine tenderness, fetal tachycardia
Key Discriminator
Painful vaginal bleeding, rigid "board-like" uterus on exam, absent fever; often associated with hypertension or trauma; no purulent fluid or signs of infection
Appendicitis in pregnancy
Why It Looks Similar
Fever, leukocytosis, abdominal pain in a pregnant patient
Key Discriminator
Right-sided abdominal pain (often shifted cephalad in later pregnancy); pain is peritoneal rather than uterine; no fetal tachycardia early on; no relation to rupture of membranes
Differential Diagnosis | Why It Looks Similar | Key Discriminator |
|---|---|---|
Epidural-related fever | Intrapartum fever after epidural placement | Isolated low-grade fever without fetal tachycardia, uterine tenderness, or foul-smelling fluid; fever onset correlates with epidural timing; no supporting lab or clinical signs of infection |
Urinary tract infection / Pyelonephritis | Fever in pregnancy, leukocytosis | Flank pain and costovertebral angle tenderness; positive urinalysis with pyuria and bacteriuria; no uterine tenderness or fetal tachycardia; often occurs antepartum rather than intrapartum |
Endometritis | Uterine tenderness, fever, polymicrobial etiology | Occurs postpartum, not intrapartum; follows delivery (particularly cesarean); uterine tenderness with lochia that may be foul-smelling; the timing distinction is the key discriminator |
Placental abruption | Uterine tenderness, fetal tachycardia | Painful vaginal bleeding, rigid "board-like" uterus on exam, absent fever; often associated with hypertension or trauma; no purulent fluid or signs of infection |
Appendicitis in pregnancy | Fever, leukocytosis, abdominal pain in a pregnant patient | Right-sided abdominal pain (often shifted cephalad in later pregnancy); pain is peritoneal rather than uterine; no fetal tachycardia early on; no relation to rupture of membranes |
06Traps and High-Yield Pearls
The most frequent way students lose points on chorioamnionitis questions is by delaying delivery while waiting for confirmatory lab results or for antibiotics to "take effect." Test writers design vignettes with a classic clinical presentation (intrapartum fever, prolonged ROM, fetal tachycardia, uterine tenderness) and then offer answer choices such as "obtain amniotic fluid culture before deciding" or "complete a 48-hour antibiotic course before delivery." Both are wrong. Once the clinical diagnosis is made, the correct sequence is start antibiotics immediately AND proceed to delivery.
The second major trap is selecting cesarean section as the delivery method for chorioamnionitis. Unless there is a concurrent obstetric indication (arrest of dilation, non-reassuring fetal status unresponsive to resuscitation, malpresentation), vaginal delivery remains the goal. The infection itself is not a reason to operate.
A third tested concept: distinguishing chorioamnionitis from epidural-associated fever. If the vignette describes a low-grade fever (38.0 to 38.4 C) developing 4 to 6 hours after epidural placement with no other clinical signs, the expected answer is continued observation, not antibiotic therapy. However, if the same patient then develops fetal tachycardia and uterine tenderness, the diagnosis shifts to chorioamnionitis regardless of the epidural.
Finally, remember the neonatal implications. A newborn delivered from a mother with chorioamnionitis requires evaluation for early-onset neonatal sepsis. This clinical connection is frequently tested to assess whether students understand that intraamniotic infection places the neonate at risk, requiring close monitoring and possible empiric antibiotics (ampicillin + gentamicin) for the infant as well.