Placental pathologic findings in preterm birth.

Microscopic features of placentas from 539 consecutive preterm deliveries and 214 term deliveries were compared. The presence of either umbilical or chorionic vasculitis was identified in 38% of the cases at 22 to 28 weeks' gestation, in 32% of the cases at 29 to 32 weeks' gestation, in 13% of the cases at 33 to 36 weeks' gestation, and in 10% of the cases at term (p less than 0.0001). Decidual vascular abnormality was present in 70% of the cases at 22 to 28 weeks' gestation, in 35% of the cases at 29 to 32 weeks, in 29% of the cases at 33 to 36 weeks, and in 15% of the cases at term (p less than 0.0001). Chronic villitis was significantly more frequent in preterm deliveries without umbilical vasculitis than in those cases with umbilical vasculitis (17% vs 8%, p less than 0.05). Our data indicate that the placental lesions of umbilical-chorionic vasculitis, decidual vascular abnormality, and chronic villitis are related to preterm birth. Umbilical-chorionic vasculitis reflects acute ascending bacterial infection. Decidual vascular abnormality has been associated with maternal autoimmune or alloimmune disorders. Chronic villitis may indicate either congenital viral infection or maternal-fetal immunopathologic conditions. Both decidual vascular abnormality and chronic villitis may reflect the activation of inflammatory mechanisms capable of leading to preterm delivery.