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Summary Table

Category	Details
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
Patient Presentation	Pregnant woman (usually intrapartum) with fever, uterine tenderness, foul-smelling amniotic fluid
Classic Physical 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
Key Diagnostic Results	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"

1. Pathophysiology

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.

2. Classification and Clinical Manifestation

The current classification system (sometimes referred to as the "Triple I" framework) stratifies intraamniotic inflammation and infection into three tiers:

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.

3. Diagnostic Workup

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.

4. Management and 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.

5. Differential Diagnosis and Distractors

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

6. Traps 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.

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