The relationship between acute inflammatory lesions of the preterm placenta and amniotic fluid microbiology

OBJECTIVE: Our objective was to determine the relationship between microbial invasion of the amniotic cavity and the presence and severity of acute inflammatory lesions in the placenta. STUDY DESIGN: Placental histologic and amniotic fluid microbiologic studies were performed in 92 consecutive patients who were admitted with preterm labor and intact membranes and delivered within 48 hours after amniocentesis. RESULTS: The prevalence of a positive amniotic fluid culture was 38% (35 of 92). There was a strong association between the presence and severity of inflammation in the amnion, chorion-decidua, umbilical cord, and chorionic plate and the results of the amniotic fluid culture (p < 0.0001 for each tissue section). Three patterns of inflammation of the chorion-decidua were identified: marginating, nonmarginating, and a mixed pattern. The marginating and the mixed patterns of inflammation were strongly associated with the presence of a positive amniotic fluid culture. Acute inflammation of the chorionic plate was the most sensitive indicator of a microbial invasion of the amniotic cavity (sensitivity 96.6%), and funisitis and umbilical vasculitis had the highest specificity (85.7%). CONCLUSION: The presence of acute inflammatory lesions of the chorioamniotic membranes can serve as a marker of microbial invasion of the amniotic cavity.