Chronic chorioamnionitis: a clinicopathologic and immunohistochemical study.

Lymphocytic inflammation of the fetal membranes is unusual and has been termed chronic chorioamnionitis. We report the clinicopathologic and immunohistochemical findings in 31 placentas with chronic chorioamnionitis. The most common histopathologic association was chronic villitis of unknown etiology, which was identified in 22 (71%) of the 31 placentas. The severity of the chronic villitis did not correlate with the severity of chronic chorioamnionitis. Additional placental findings included chronic intervillositis in two, fetal vessel thrombosis in five, hemorrhagic endovasculitis in four, decidual chronic vasculitis in three, and atherosis in one. Maternal history included pregnancy-induced hypertension in six and diabetes in one. Twelve infants were preterm, and five had intrauterine growth retardation. There was no neonatal sepsis or death. Immunohistochemical staining in areas of chronic chorioamnionitis showed CD3+ and CD8+ cells present in moderate numbers, and CD4+ cells in smaller numbers. CD20+ and CD56+ cells were rare or absent. Chronic chorioamnionitis is commonly associated with chronic villitis of unknown etiology, shares similar clinical associations, and may have a related cause, possibly immunologic.