In 2003, a Cochrane meta-analysis of 5 studies involving 622 women with previous preterm birth showed a decrease in the risk of low birth weight infants born to women receiving antibiotics vs placebo for the treatment of BV (odds ratio [OR]=0.31; 95% CI, 0.13–0.75).6 Treatment also decreased the risk of preterm-prelabor rupture of membranes (OR=0.14; 95% CI, 0.05–0.38) compared with placebo. Unfortunately, these studies did not always specify whether women were asymptomatic for BV infection. In many of the trials, symptomatic women were excluded as they were automatically treated with antibiotics.
In 2003, 2 RCTs evaluating the early treatment of asymptomatic BV in low- and high-risk patients showed a decrease in preterm labor. The first RCT included 494 asymptomatic pregnant women who presented for prenatal care between 12 and 22 weeks gestation. If women had BV detected by Gram stain using Nugent’s criteria, they were randomized to receive either 300 mg oral clindamycin twice daily for 5 days or placebo. In the general population, treatment with clindamycin reduced the rate of late miscarriage and spontaneous preterm delivery by 10.4% (95% CI, 5.0–15.8). In women with a previous preterm delivery or a late miscarriage the proportion of preterm delivery or late miscarriage was reduced (16.6% vs 42%).7
The second RCT included 409 asymptomatic women between 13 and 20 weeks gestation with BV by Gram stain using Nugent’s criteria. Investigators randomized women to intravaginal clindamycin each night for 3 days. At a second visit, 20 to 24 days after treatment, women were retested for BV and if they were positive, they received a 7-day course of intravaginal clindamycin or placebo based on the previous randomization. In this study, the incidence of preterm birth was reduced from 10% to 4% (relative risk [RR]=0.38; 95% CI, 0.16–0.90; NNT=17). This study only included 21 women with previous preterm delivery and a subgroup analysis was not performed.8
Intravaginal clindamycin has been associated with worse pregnancy outcomes for patients who do not have bacterial vaginosis. A randomized trial of the prophylactic intravaginal clindamycin 2% cream to prevent preterm birth in high-risk women showed an increase in spontaneous preterm delivery in women who actually used all of the medication and did not have BV (NNH=12.3; P<.05).9
Recommendations from others
The US Preventive Services Task Force concludes that the evidence is insufficient to recommend for or against routinely screening for BV for high-risk pregnant women. Furthermore, they recommend against screening for average risk women.10
The Centers for Disease Control and Prevention recommends that high-risk pregnant women (eg, those women who have had a previous preterm delivery) with asymptomatic BV may be evaluated for treatment. The recommended treatment regimens are metronidazole 500 mg orally twice a day for 5 days, metronidazole gel intravaginally for 5 days, or clindamycin cream intravaginally for 7 days.11
The Cochrane Pregnancy and Childbirth Group finds no evidence supporting routine screening and treatment for asymptomatic bacterial vaginosis in pregnancy, except possibly for women with a history of preterm birth.6
The American College of Obstetrics and Gynecology summarizes no data supports screening for BV to prevent preterm birth. Their bulletin references a subgroup of women with previous preterm birth who did show benefit from treatment for BV, but the authors speculated that reanalysis with the inclusion of the largest trial to date, which did not show a benefit for this subgroup, might nullify these results.12
CLINICAL COMMENTARY
Until there’s more research, only screen women who are high-risk or symptomatic
Grace Alfonsi, MD
Denver Health, Denver, Colo
Although the association of BV and chorioamnionitis and preterm labor is strong, the RCTs do not show any change in outcomes by screening and treating asymptomatic BV in pregnancy except in women who already have a history of preterm labor or premature rupture of membranes. Our practice was screening and treating all pregnant women at the first prenatal visit until about 3 years ago when the RCTs failed to show an impact. The studies that brought BV to the forefront of this discussion show that the inflammatory response caused by BV start in the first trimester or before and treatment is most effective when done early. Perhaps these RCTs are not treating enough women early in pregnancy to see a difference in outcome.
The study we need to have (and which may never be done) would test the treatment of women with BV, either just before conception or early in the first trimester. I am awaiting the next round of information, but for now, I only screen women who are high risk or women who are symptomatic.