45 Asymptomatic bacterial vaginosis
Bacterial vaginosis results from the relative deficiency of normal Lactobacillus species in the vagina and relative overgrowth of anaerobic bacteria. Identifying and treating bacterial vaginosis does not appear to change the risk of preterm birth or other pregnancy complications.
As identifying and treating asymptomatic bacterial vaginosis does not appear to change the risk of preterm birth or other pregnancy complications, routine testing in pregnancy is not appropriate.
Bacterial vaginosis results from the relative deficiency of normal Lactobacillus species in the vagina and relative overgrowth of anaerobic bacteria. This reduces the normal acidity of the vagina. Bacterial vaginosis is asymptomatic for 50% of women in pregnancybut may result in a vaginal discharge that can be grey in colour with a characteristic ’fishy’ odour .
45.1.1 Asymptomatic bacterial vaginosis in pregnancy
- Several large prospective, longitudinal studies have found the prevalence of bacterial vaginosis to be in the range 9–23% . A study in remote central Australia (n=205) found a prevalence of 26–36% among women attending clinics for a women’s health assessment (for either a symptomatic episode or routine check but not for antenatal care).
- Risk factors: Bacterial vaginosis in pregnancy is more common among women of low socioeconomic status and women who had low birth weight babies in previous pregnancies (Hillier et al 1995, French et al 2006).
45.1.2 Risks associated with asymptomatic bacterial vaginosis in pregnancy
Bacterial vaginosis has been associated with an increased risk of preterm birth CI 1.62–2.11) to give birth preterm than women without . The higher risk of preterm birth remains in women diagnosed with bacterial vaginosis early in pregnancy, even if the bacterial vaginosis spontaneously resolves later in pregnancy ., with a review of case–control and cohort studies finding that women with bacterial vaginosis were 1.85 times more likely (95%
45.2 Testing for asymptomatic bacterial vaginosis
Routine testing for asymptomatic bacterial vaginosis in pregnancy is not recommended in the United Kingdom, the United States or Canada . The systematic review supporting the United States statement found that:
- no studies directly addressed the adverse effects of testing pregnant women who are asymptomatic for bacterial vaginosis
- there is no clear benefit for the general population from testing and treating asymptomatic bacterial vaginosis during pregnancy
- although a subgroup of high-risk women may benefit from testing and treatment for bacterial vaginosis in pregnancy, a sizeable group would receive either no benefit or may experience harm.
45.2.1 Diagnosis of bacterial vaginosis
Bacterial vaginosis is generally diagnosed by either:
- Amsel’s criteria (thin white-grey homogenous discharge, pH greater than 4.5, release of ‘fishy odour’ on adding alkali, clue cells present on direct microscopy) ; or
- Nugent’s criteria (Gram-stained vaginal smear to identify proportions of bacterial morphotypes with a score of greater than six indicating bacterial vaginosis) , which has both high sensitivity and specificity , does not seem to vary with the vaginal site of collection and has greater sensitivity than standard antenatal clinical diagnosis or a commercial test .
Other forms of testing, including the pH/whiff test or QuickVue Advanced pH and Amines test, have not been found to be reliable in detecting asymptomatic bacterial vaginosis in pregnancy.
45.2.2 Effect of treatments on risks associated with bacterial vaginosis
While antibiotics are effective in eradicating bacterial vaginosis, treatment does not change the risk of preterm birth, low birth weight or premature rupture of the membranes in women at low risk of preterm birth. The Cochrane review (McDonald et al 2007) found:
- no statistically significant decrease in the risk of preterm birth at less than 37 weeks gestation for any treatment versus no treatment or placebo (n=5,888; OR 0.91; 95% CI 0.78–1.06)
- no evidence of an effect on birth before 34 weeks (n=851; OR 1.22; 95% CI 0.67–2.19) or birth before 32 weeks (n=3,565; OR 1.14; 95% CI 0.76–1.70)
- no difference in the incidence of low birth weight (n=4,107; OR 0.95; 95% CI 0.77–1.17)
- no decrease in the risk of preterm rupture of membranes (n=2,579; OR 0.88; 95% CI 0.61–1.28)
- a possible reduction in risk of preterm birth if treatment is given before 20 weeks pregnancy (n=2,387; OR 0.72; 95% CI 0.55–0.95).
In women with a previous preterm birth, treatment did not affect the risk of subsequent preterm birth (n=622; OR 0.83; 95% CI 0.59–1.17). However, two small studies showed a decrease in the risk of preterm rupture of the membranes (OR 0.14; 95% CI 0.05–0.38) and low birth weight (OR 0.31; 95% CI 0.13–0.75; n=114).
Although there is no evidence that testing and treating all women with bacterial vaginosis in the antenatal period will have a major impact on the rate of preterm birth, there is emerging evidence that early treatment may be more effective.
Do not routinely offer pregnant women testing for bacterial vaginosis.
Approved by NHMRC in December 2011; expires December 2016
Early treatment (before 20 weeks pregnancy) of proven bacterial vaginosis may be beneficial for women with a previous preterm birth.
Approved by NHMRC in December 2011; expires December 2016
45.3 Practice summary: testing for bacterial vaginosis
In the antenatal period.
- Aboriginal and Torres Strait Islander health worker
- multicultural health worker.
- Document and follow-up
If a woman is tested for bacterial vaginosis, note the results in her record. Have a system in place so that women who test positive are given information about treatments.
- BASHH (2006) National Guideline for the Management of Bacterial Vaginosis. Clinical Effectiveness Group, British Association for Sexual Health and HIV.
- SOGC (2008) Screening and Management of Bacterial Vaginosis in Pregnancy. SOGC Clinical Guideline No 211. Infectious Diseases Committee and approved by the Executive and Council of the Society of Obstetricians and Gynaecologists of Canada.
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- Smith KS, Tabrizi SN, Fethers KA et al (2005) Comparison of conventional testing to polymerase chain reaction in detection of Trichomonas vaginalis in indigenous women living in remote areas. Int J STD AIDS 16: 811–15.
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