The association of chorioamnionitis with preterm delivery.

To ascertain what proportion of preterm deliveries are attributable to the association with chorioamnionitis, the authors examined prospectively the placentas from all 2774 women who delivered at the Johns Hopkins Hospital during 1980. The incidence of preterm delivery was 5.4% (110 of 2027) when neither chorioamnionitis nor premature rupture of membranes (PROM) was present, 11.9% (29 of 243) when chorioamnionitis was present without PROM, and 56.7% (51 of 90) when both chorioamnionitis and PROM were present (P less than .05). Only 27 of 333 cases of histopathologic chorioamnionitis or 8.1% had maternal antepartum fever, and only 11 of 333 or 3.3% had neonatal sepsis. Using logistic regression analysis to control for confounding variables, approximately 25% of the preterm deliveries were statistically attributable to histopathologic chorioamnionitis, occurring either alone or in association with PROM. In light of the infrequency with which histopathologic chorioamnionitis is clinically evident, the strong relationship between histopathologic chorioamnionitis and preterm delivery suggests that occult antepartum infection of the genital tract is an important cause of preterm delivery.