The pH level of the normal vagina is lower than 4.5, which is maintained by the production of lactic acid. Estrogen-stimulated vaginal epithelial cells are rich in glycogen. Vaginal epithelial cells break down glycogen to monosaccharides, which can be converted by the cells themselves, and lactobacilli to lactic acid.
Normal vaginal secretions are ﬂoccular in consistency, white in color, and usually located in the dependent portion of the vagina (posterior fornix). Vaginal secretions can be analyzed by a wet-mount preparation. A sample of vaginal secretions is suspended in 0.5 mL of normal saline in a tube, transferred to a slide, covered with a slip, and assessed by microscopy. Some clinicians prefer to prepare slides by suspending secretions in saline placed directly on the slide. Secretions should not be placed on the slide without saline because this method causes drying of the vaginal secretions and does not result in a well-suspended preparation. Microscopy of normal vaginal secretions reveals many superficial epithelial cells, few white blood cells (less than 1 per epithelial cell), and few, if any, clue cells. Clue cells are superficial vaginal epithelial cells with adherent bacteria, usually Gardnerella vaginalis, which obliterates the crisp cell border when visualized microscopically. Potassium hydroxide 10% (KOH) may be added to the slide, or a separate preparation can be made, to examine the secretions for evidence of fungal elements. The results are negative in women with normal vaginal microbiology. Gram stain reveals normal superficial epithelial cells and a predominance of gram-positive rods (lactobacilli).
Bacterial Vaginosis Bacterial vaginosis (BV) is an alteration of normal vaginal bacterial ﬂora that results in the loss of hydrogen peroxide–producing lactobacilli and an overgrowth of predominantly anaerobic bacteria (3,4). The most common form of vaginitis in the United States is BV (5). Anaerobic bacteria can be found in less than 1% of the ﬂora of normal women. In women with BV, however, the concentration of anaerobes, and G. vaginalis and Mycoplasma hominis, is 100 to 1,000 times higher than in normal women. Lactobacilli are usually absent.
It is not known what triggers the disturbance of normal vaginal ﬂora. It is postulated that repeated alkalinization of the vagina, which occurs with frequent sexual intercourse or use of douches, plays a role. After normal hydrogen peroxide–producing lactobacilli disappear, it is difficult to reestablish normal vaginal ﬂora, and recurrence of BV is common.
Numerous studies show an association of BV with significant adverse sequelae. Women with BV are at increased risk for pelvic inﬂammatory disease (PID), postabortal PID, postoperative cuff infections after hysterectomy, and abnormal cervical cytology (6–9). Pregnant women with BV are at risk for premature rupture of the membranes, preterm labor and delivery, chorioamnionitis, and postcesarean endometritis (10,11). In women with BV who are undergoing surgical abortion or hysterectomy, perioperative treatment with metronidazole eliminates this increased risk (12,13).
Diagnosis Office-based testing is required to diagnose BV. It is diagnosed on the basis of the following findings (14): 1.
A fishy vaginal odor, which is particularly noticeable following coitus, and vaginal discharge are present.
2.
Vaginal secretions are gray and thinly coat the vaginal walls.
3.
The pH of these secretions is higher than 4.5 (usually 4.7 to 5.7).
4.