Infectious conditions

Topic Completed: 1 September 2011

Revised: 22 July 2019

Copyright: 2002-2019,, Inc.

PubMed Search: Placenta chorioamnionitis[title] "loattrfree full text"[sb]

Mandolin S. Ziadie, M.D.
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Cite this page: Ziadie MS. Chorioamnionitis. website. Accessed September 17th, 2019.
Definition / general
  • Maternal inflammatory response usually due to ascending bacterial infection by group B streptococci, Listeria monocytogenes and Fusobacterium (Fusobacterium caused 18% of cases, detect with Warthin-Starry stain, Arch Pathol Lab Med 1985;109:739)
  • Two or more microbes are common
  • May cause premature rupture of membranes
  • Major cause of fetal / neonatal infection, stillbirth, prematurity and perinatal morbidity and mortality
Clinical features and diagnosis
  • Maternal temperature > 37.8 C plus two of the following: maternal or fetal tachycardia, uterine tenderness, foul amniotic fluid odor or leukocytosis
  • Clinical features have poor specificity and sensitivity for prediction of histologic chorioamnionitis
  • Associated with premature rupture of membranes
  • Associated with occult congenital syphilis in stillborn (Arch Pathol Lab Med 1994;118:44)
  • More frequent and severe with younger gestational age
  • Note: fetal hypoxia and meconium staining of membranes do NOT cause inflammatory changes in placenta
Stage 1 (mild): acute subchorionitis / acute chorionitis:
  • Neutrophils in subchorionic fibrin or interface between deciduas and chorion

Stage 2 (moderate): acute chorioamnionitis:
  • Neutrophils in connective tissue plane between chorion and amnion

Stage 3 (severe): necrotizing chorioamnionitis:
  • Necrosis, amnion sloughing, thickening of amnion basement membrane and neutrophilic karyorrhexis
  • Multifocal abcesses may be present
Gross description
  • Dull, opaque membranes with yellow green discoloration and cloudy amniotic fluid, possibly with purulent exudate
  • May be grossly normal
Microscopic (histologic) description
  • Neutrophilic infiltrate of free membranes and those overlying the chorionic plate
  • Variable fetal response including funisitis and chorionic plate vasculitis
  • May have acute intervillositis (often due to Listeria monocytogenes) or peripheral funisitis (often due to candida)
Microscopic (histologic) images

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Acute inflammation

Acute exudative
inflammation present
with microabscess
formation in decidua

Subacute chorioamnionitis
  • May indicate long standing infection by pathogens of low virulence
  • Prolonged (subacute) inflammation with amniotic necrosis is associated with chronic lung disease (bronchopulmonary dysplasia, Wilson-Mikity syndrome, Hum Pathol 2002;33:183)
  • Mixed cell infiltrate of mononuclear cells and neutrophils, primarily in the amnion and upper chorion
Chronic chorioamnionitis
  • Rare; etiology unknown
  • Primarily lymphocytic infiltration of chorioamnion, associated with chronic villitis of unknown etilogy (71%), maternal hypertension (20%), preterm infants (40%) and intrauterine growth restriction (15%) (Hum Pathol 1998;29:1457)
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