Value of placental microbial evaluation in diagnosing intra-amniotic infection

OBJECTIVE: To evaluate the ability of microbiologic and pathologic examination of the placenta to accurately diagnose intraamniotic infection and inflammation. METHODS: One hundred eighty-three women with a clinically indicated amniocentesis were enrolled prospectively. We applied our analysis to 56 women with evidence of preterm labor or preterm premature rupture of membranes who delivered within 48 hours of amniotic fluid testing results. Twenty-three patients, assessed for fetal lung maturity in the third trimester, served as controls. Amniotic fluid was cultured for aerobic, anaerobic, Ureaplasma, and Mycoplasma species. We used mass spectrometry to assess the degree of intraamniotic inflammation (Mass Restricted scoring). After delivery, microbiologic and histologic studies of the placenta were performed. These results were interpreted in comparison with the direct microbiologic and inflammatory analysis of the amniotic fluid. A sample size of 45 patients was required to show a test accuracy of 80% or more. RESULTS: Ninety-two percent of women with positive amniotic fluid cultures tested with at least one positive placenta culture. Eighty percent of women who had negative amniotic fluid cultures also tested with a positive placenta culture. The accuracy of placental cultures in predicting amniotic fluid infection varied from 44% to 57%. Placental pathology showed an accuracy of only 58% in diagnosing intraamniotic inflammation. CONCLUSION: Placental microbiologic and histologic studies poorly reflect the infectious and inflammatory status of the amniotic fluid. Results of such studies should be interpreted with caution in the management and future counseling of women with preterm labor or preterm premature rupture of membranes.