Examining the Evidence
Does treating asymptomatic bacterial vaginosis reduce preterm delivery?
Sometimes. In a meta-analysis for the US Preventive Services Task Force, screening and treatment for bacterial vaginosis (BV) of pregnant women at low or average risk of preterm delivery did not prolong pregnancy. A slight benefit was seen in women at high risk of preterm birth.
BV is one of the most prevalent vaginal disorders, affecting 30% of women of reproductive age.1 The syndrome is characterized by a relative lack of lactobacillus and increased anaerobes, Gardnerella vaginalis, Mobiluncus species, and Mycoplasma hominis. A strong and consistent association exists between BV during pregnancy and spontaneous preterm birth and amniotic fluid infection.2,3
Data were collected with rigor and detail
In this meta-analysis, designed to update 2001 recommendations from the US Preventive Services Task Force, Nygren and colleagues augmented the earlier data with published English-language studies from Ovid Medline (2000 through September 2007) and Cochrane Library databases (through September 2007), reference lists, and expert suggestions. The authors are to be applauded for the rigor and detail with which they collected source data. They used these data to estimate the pooled effect of treatment of BV on preterm delivery (at <37, <34, and <32 weeks’ gestation), low birth weight, and preterm, premature rupture of membranes among women at low, average, and high risk of preterm birth.
Heterogeneity of studies was a problem
It usually is difficult to pool studies because of major differences in study design, inclusion and exclusion criteria, diagnostic criteria, assessment of risk status, and treatment. This is particularly true in regard to studies of women at high risk for preterm birth. The authors acknowledge this heterogeneity and considered it in statistical analysis of the data, but the detection of significant benefit or harm for BV screening and treatment remained difficult.
More study is needed
More research certainly is needed to elucidate the relationship between vaginal flora and preterm birth among high-risk women. We currently lack the ability to identify particular subgroups of women with abnormal vaginal flora who are most likely to derive benefit from screening and treatment.
What this evidence means for clinical practice
Treating pregnant women at low or average risk of preterm birth for asymptomatic BV is not beneficial. This conclusion is well supported by the findings of Nygren and colleagues as well as other studies.
As for high-risk women, screening and treatment are reasonable based on current knowledge, although the data are inconclusive. In this study, three trials demonstrated a reduction in preterm birth with treatment, but one trial demonstrated harm and one trial found no benefit.—Hyagriv N. Simhan, MD, MSCR
1. Allsworth JE, Peipert JF. Prevalence of bacterial vaginosis: 2001–2004 National Health and Examination Survey data. Obstet Gynecol. 2007;109:114-120
2. Hillier SL, Krohn MA, Cassen E, Easterling TR, Rabe LK, Eschenbach DA. The role of bacterial vaginosis and vaginal bacteria in amniotic fluid infection in women in preterm labor with intact fetal membranes. Clin Infect Dis. 1995;20 Suppl;2:S276-S278
3. Meis PJ, Goldenberg RL, Mercer B, et al. The preterm prediction study: significance of vaginal infections. National Institute of Child Health and Human Development Maternal–Fetal Medicine Units Network. Am J Obstet Gynecol. 1995;173:1231-1235