Chronic villitis, chronic chorioamnionitis, and maternal floor infarction.

Chronic inflammatory infiltrates in the human placenta are much less common than acute inflammation. Most often, chronic inflammation is found in the villi (villitis), but rarely it may involve the fetal membranes. Villitis is associated with many well-documented maternal infections. Reviewed herein are features of the villous inflammatory infiltrate and associated villous changes that may suggest a specific bacterial or protozoal etiology. However, the majority of villitides are of unknown etiology. These may be the result of an unrecognized pathogen or, alternatively, may reflect an abnormal immune reaction. Chronic chorioamnionitis is commonly associated with villitis and has accompanied some well-documented viral, bacterial, and protozoal infections, but a specific infectious etiology is not identified in many cases. Maternal floor infarction is not a true infarct; it is characterized by the deposition of fibrin in the decidua basalis and intervillous space where enveloped villi become avascular and sclerotic. Maternal floor infarction is associated with intrauterine growth retardation and fetal demise. It frequently recurs in successive pregnancies.