This prospective comparative study evaluated a DNA hybridization test (Affirm VPIII) as an alternative to Gram stain for the diagnosis of bacterial vaginosis. We examined vaginal smears from 1,725 pregnant women between the 12th and 36th weeks of gestation with clinical signs of vaginal infection. The DNA hybridization test compared well with Gram stain and can be used as a rapid diagnostic tool to exclude bacterial vaginosis.Common reproductive tract infections and associated inflammatory responses are the most frequent gynecological complaints, representing a central problem in modern clinical care. Vaginitis is usually characterized by vaginal discharge, vulvar itching and irritation, or odor. Even though the causative microorganisms are manifold, the three diseases most frequently associated with vaginitis are bacterial vaginosis, vulvovaginal candidiasis, and trichomoniasis (3). The complications of bacterial vaginosis can be especially substantial in pregnant women, increasing the risk of an adverse pregnancy outcome, including histological chorioamnionitis (5), amniotic fluid infection (12), preterm labor, and preterm delivery (8, 9). Laboratory methods for the identification of bacterial vaginosis include wet mount, Gram stain, the "gold standard" of diagnosis, and microbiological culture. Because microscopic evaluation by wet mount or Gram stain requires special diagnostic skills not available to all practitioners, overdiagnosis is common and therapy is frequently empirical. Although cultures for Gardnerella vaginalis constitute a highly sensitive method, they are not recommended for the diagnosis of bacterial vaginosis due to the high number of women positive for G. vaginalis who do not have clinical symptoms of bacterial vaginosis (2, 6). Furthermore, determination of G. vaginalis by culture is rarely useful because of the relatively long period between the examination and the time the results are finally available. Because the different forms of vaginitis call for different treatment regimens, there is a need for a rapid and highly selective tool to help the care provider diagnose bacterial vaginosis and distinguish it from other types of infection. The aim of this study was to evaluate a DNA hybridization test (Affirm VPIII) as an alternative to Gram-stained microscopic slides, currently considered the most reliable diagnostic tool.This study on the prospective comparison of two diagnostic tools included 1,725 pregnant women between the 12th and 36th weeks of gestation attending the outpatient clinic of the Department of Obstetrics and Gynecology at the University of Vienna, Vienna, Austria. If clinical symptoms such as increased vaginal discharge combined with pruritus and/or burning, cervical incompetence, lower abdominal pain, preterm labor, or preterm rupture of the membranes were present, two vaginal specimens were obtained with the Affirm VPIII sample collection set on Dacron tipped swabs for both Gram stain and nucleic acid hybridization. The samples were immediately transported to the labora...