This is not an actual vaginal infection but rather a clinical syndrome resulting from replacement of the normal H2O2-producing Lactobacillus species with high concentrations of anaerobic bacteria (e.g., Prevotella and Mobiluncus species), Gardnerella vaginalis, and Mycoplasma hominis. Bacterial vaginosis (BV) is a common cause of vaginal discharge or malodor, however, as many as half of women are asymptomatic. The pathophysiology of the microbial interactions is not fully understood, particularly in pregnancy (Nelson and Macones, 2002).

It is unclear whether BV is a sexually transmitted syndrome, but it is rare among women who have never been sexually active. Treatment of the male sex partner has not been beneficial in preventing the recurrence of BV.

DIAGNOSIS.
BV can be diagnosed by clinical criteria or by Gram stain. The clinical criteria of Amsel require at least three of the following symptoms or signs:

1. Homogeneous, white, noninflammatory discharge that smoothly coats the vaginal walls.

2. Presence of clue cells on microscopic examination.

3. Vaginal fluid pH greater than 4.5.

4. Fishy odor of discharge before or after addition of 10-percent potassium hydroxide -  the whiff test.

When a Gram stain is applied to the discharge, assessment of the relative concentration of bacterial morphotypes characteristic of the altered flora is an acceptable laboratory method for diagnosing BV -  the Nugent criteria. Cervical Papanicolaou tests have limited clinical usefulness for the diagnosis of BV because of low sensitivity.

TREATMENT.
All symptomatic pregnant women should be tested and treated. A number of studies have shown that BV is associated with adverse pregnancy outcomes. These include prematurely ruptured membranes, preterm labor, preterm birth, chorioamnionitis, and postabortion and postpartum pelvic infection. Unfortunately, prospective studies have shown no improvement of perinatal outcomes with treatment.

Therapy for symptomatic BV in pregnant women may have other benefits such as reduction of the risk for sexually transmitted infections. The optimal regimen for women during pregnancy is not known, but the oral metronidazole regimens shown in

Table 59-8 probably are equally effective. Cure rates with these are about 70 percent (Koumans and associates, 2002). The clindamycin and topical regimens are less effective. There have been no consistent association between metronidazole and teratogenic or mutagenic effects in newborns.

FOLLOW-UP.
If symptoms resolve, no further evaluation is needed. Recurrence of symptomatic BV is not unusual, and additional therapy is given with another listed regimen. Routine treatment of sex partners is not recommended.