Vaginal Indicators of Amniotic Fluid Infection in Preterm Labor

Objective: To determine whether vaginal interleukin-6, interleukin-8, neutrophils, bacterial vaginosis, and selected vaginal bacteria are predictors of amniotic fluid (AF) infection among women in preterm labor.

Methods: One hundred ninety-seven afebrile women in preterm labor with intact membranes had vaginal and AF samples collected for Gram stain, culture, and interleukin-8 and interleukin-6 determinations. Vaginal interleukin-6, interleukin-8, neutrophils, and vaginal flora were compared in women with positive and negative AF cultures. The negative AF culture group was subdivided according to AF interleukin-6 concentration. Logistic regression was used to examine the associations between vaginal cytokines and flora and AF infection or elevated AF interleukin-6.

Results: The vaginal interleukin-8 concentration and neutrophil count were significantly higher with both AF infection and elevated concentrations of AF interleukin-6 and interleukin-8. The vaginal interleukin-6 concentration was not associated with AF infection or high concentration of AF cytokines. Amniotic fluid infection was associated with bacterial vaginosis or intermediate vaginal flora by Gram stain, absence of hydrogen peroxide-producing Lactobacillus, and presence of vaginal Bacteroides ureolyticus and Fusobacterium. Vaginal interleukin-8 levels greater than 30 ng/mL had 80% sensitivity and a positive predictive value of 35%, and an abnormal vaginal Gram stain (more than five neutrophils per 400x field, bacterial vaginosis species, or intermediate flora) had 90% sensitivity and a positive predictive value of 27% to detect AF infection or elevated AF interleukin-6.

Conclusion: A high vaginal interleukin-8 concentration, abnormal vaginal Gram stain, absent hydrogen peroxide-producing Lactobacillus, and anaerobic vaginal flora were strongly associated with AF infection among women in preterm labor.