Association of abnormal vaginal flora and Ureaplasma species as risk factors for preterm birth: a cohort study.

OBJECTIVE: To find out whether the presence of Ureaplasma species (U. spp.) in combination with an alteration of the normal vaginal flora is an independent risk factor for preterm delivery. DESIGN: Prospective observational study. SETTING: Department of Obstetrics, University Hospital in Brussels. POPULATION: A total of 1,988 singleton pregnancies were included. METHODS: From each woman, a cervical culture for U. spp. was obtained and the vaginal flora evaluated at the first prenatal visit. The presence of known risk factors for preterm delivery was recorded. Preterm birth was defined as delivery <37 weeks. RESULTS: There were 97 (4.9%) preterm births. In patients delivered before 37 weeks, abnormal vaginal flora was detected in 22.7% and U. spp. in 53.6% of these. The conditions were found together in 17.5%. In patients delivered at term, an abnormal vaginal flora was detected in 14.4% and U. spp. in 41.4% of these women, while they co-existed in 8.2%. Using a logistic regression analysis taking into account known risk factors for preterm birth and the microbiological parameters, preterm delivery was correlated with the presence of U. spp. (odds ratio (OR) 1.64; 95% confidence interval (CI) 1.08-2.48; p = 0.02) and abnormal vaginal flora in combination with U. spp. (OR 2.35; 95% CI 1.35-4.10; p = 0.003). No significant correlation between the presence of abnormal vaginal flora and preterm delivery (p = 0.09) was found. CONCLUSIONS: Preterm delivery was significantly correlated with the presence of U. spp. The risk for preterm delivery increased when U. spp. was associated with an abnormal vaginal flora.