Objective: We sought to determine the predictors of intraamniotic infection with use of the presence or absence of vaginal microbes and clinical variables.
Study design: Vaginal fluid was collected and analyzed on 936 of 2711 (35%) consecutive patients who were delivered over a 7-month period. Subjects were followed up prospectively for the development of intraamniotic infection. Intraamniotic infection was defined as an intrapartum fever > 37.8 degrees C plus at least two of the five following variables: maternal or fetal tachycardia, leukocytosis, tender uterus, or foul-smelling amniotic fluid. Bacterial vaginosis score and the presence or absence of aerobic vaginal organisms were independent microbial variables. Demographic, maternal, labor, and delivery characteristics were independent clinical variables. Stepwise logistic regression analysis was used to develop adjusted odds ratios for predicting intraamniotic infection (expressed as odds ratio [95% confidence interval]). Selection bias and microbiologic reliability were measured.
Results: A bacterial vaginosis score of 7 to 10 (odds ratio 1.7, [95% confidence interval 1.0 to 3.9]), nulliparity (2.1 [1.3 to 3.4]), each hour of internal fetal electrode (1.2 [1.0-1.3]); and, each vaginal examination (1.7 [1.0-3.9]) were predictors of intraamniotic infection. Selected aerobic vaginal organisms such as group B streptococci or gram-negative rods were not predictive. Reanalysis with a bacterial vaginosis score > or = 4 revealed similar predictors of intraamniotic infection. Bacterial vaginosis had an adjusted odds ratio of 1.85 (1.16 to 2.9). Selected higher risk populations, vaginal examinations > or = 6 (n = 365), or rupture of membranes > or = 7 hours (n = 421) did not change the risk of a bacterial vaginosis score > or = 4 (adjusted odds ratio 1.87 and 1.98, respectively).
Conclusion: Abnormal vaginal flora combines with clinical variables to increase the risk of intraamniotic infection.