A microbiologic and clinical study of placental inflammation at term.

This study describes the relationships between histologically evident inflammation of the placenta, membranes, and umbilical cords, and correlates these lesions with clinical outcome and with amniotic fluid and amniotic membrane cultures in pregnancies at risk for clinical infection. The overall frequency of inflammation in 123 placentas was 85.45%. There were good interrelationships between inflammatory lesions at various sites. Membrane infiltrates of 3+ were seen in 90.9% of intra-amniotic infection cases, but in only 18.4% of asymptomatic patients (P less than .001). Conversely, 76.9% of patients with 3+ inflammation had intra-amniotic infection, whereas only 7% with lesser degrees of inflammation had intra-amniotic infection. Inflammation of any degree (1-3+) had a low specificity (28%) for febrile maternal outcome. Bacteria were recovered in 117 (95.1%) of the amniotic fluids. The grade of histologic lesions was associated with total colony count of bacteria in amniotic fluid (P less than .05) and with high-virulence bacteria in amniotic fluid (P less than .05), and Mycoplasma hominis in amniotic fluid (P less than .05). Bacteria were found in 67.6% and mycoplasmas in 18.6% of amniotic membrane cultures. Chlamydia trachomatis was not recovered in any of 35 amniotic membrane cultures. No significant correlation was seen between organisms in the amniotic membrane and histologic inflammation. Thus, positive amniotic fluid culture results are associated with histologic inflammation, and may cause the inflammatory response. A logistic regression model revealed that predictors of histologic inflammation include maternal diagnosis, amniotic fluid colony count, and M hominis in amniotic fluid.