Histologic chorioamnionitis, microbial infection, and prematurity.

The purpose of this study was to relate histologic chorioamnionitis to the isolation of microorganisms from the freshly separated chorioamnion in women who had early preterm delivery (before 35 weeks' gestation) following spontaneous labor. Histologic chorioamnionitis was identified in 51 of 95 study subjects. It was more common in the second trimester (72%) than from 27-34 weeks' gestation (33%) (P less than .001). Culture specimens were obtained for aerobic and anaerobic bacteria, yeasts, mycoplasmas, and Chlamydia. Microorganisms were recovered from 38 subjects; all culture reports were negative in 36. A statistically significant association was demonstrated between histologic chorioamnionitis and positive culture results. If any microorganism was recovered, 68% of the subjects had histologic chorioamnionitis, versus 39% if all cultures were negative. Of cases of histologic chorioamnionitis in the third trimester, 92% were associated with positive cultures, compared with 54% in the second trimester. Our results suggest that histologic chorioamnionitis is not synonymous with infection, especially in the second trimester.