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Summary of Benefits and Harms

In summary, there appears to be no benefit to screening and treating for BV in the general population of pregnant women. The findings for average-risk women are consistent with those of a recent Cochrane review of treatment of BV in pregnancy (15). We similarly found no benefit to screening all women at high risk for preterm delivery (women with a previous preterm delivery) for the clinically important outcomes of preterm delivery prior to 34 weeks, low birth weight less than 2500 grams, and preterm premature rupture of membranes.

The finding of benefit in some high-risk studies suggests that there may be a subgroup of high-risk women that may benefit from screening for BV in pregnancy. Table 3 summarizes our estimates of the consequences of screening for BV in 1000 patients from the general high-risk population and 1000 from a more selected population. The base case for the general high-risk population incorporates the mean and 90% CIs from the NICHD study (39) for the listed outcomes. The second scenario incorporates the pooled results of three other high-risk studies (36-38). Of note, all studies used in this balance sheet used metronidazole therapy. In the base case, we assumed that treating these women for BV reduces their risk of adverse pregnancy outcomes to that of BV-negative women (i.e., the maximum plausible effect), as well as a worst-case scenario, using the lower 90% CI of the pooled estimate. In both scenarios we also assumed that metronidazole therapy might be associated with a higher rate of preterm delivery less than 34 weeks in high-risk patients without BV, because the only trial of these four that examined this effect found a clinically and statistically significant harmful effect (37). We also assumed that the screening test has a sensitivity of 95% and specificity of 95%, the prevalence of unsuspected BV is 25%, and that adherence to treatment is 80%.

In the general high-risk population, of 1000 women screened, 238 are correctly diagnosed to have BV, and 190 of these complete therapy. With screening and treatment there would be 14 additional preterm deliveries before 37 weeks (90% CI=7 fewer to 36 additional cases), 8 additional cases of preterm premature rupture of membranes (90% CI=4 fewer to 19 additional cases), and 2 fewer preterm deliveries before 34 weeks (90% CI=14 fewer to 11 additional cases).

In the second high-risk group, screening and treatment results in 42 fewer preterm deliveries before 37 weeks (90% CI=25 to 59), 49 fewer cases of preterm premature rupture of membranes (90% CI=28 to 70), and 9 fewer cases (90% CI=19 fewer to 2 additional cases) of preterm delivery before 34 weeks per 1000 women screened. One case of preterm delivery at less than 34 weeks would be prevented for every 111 patients screened; likewise, one case of preterm delivery at less than 37 weeks would be prevented for every 24 (90% CI=17 to 40) patients screened. Because we assumed a potential increase in preterm delivery before 34 weeks in BV-negative patients, the effect of screening on preterm delivery less than 34 weeks is moderately sensitive to changes in the accuracy of the screening test. In the more selected high-risk group, for example, screening and treatment result in an increase in preterm delivery before 34 weeks if the specificity of the screening test for BV is below 80% (not shown).


There are several issues of generalizability to consider to determine whether screening and treating for BV may be useful for patients. First, all U.S. studies were conducted in tertiary referral centers or public health clinics and may not be generalizable to community-based practices. Second, screening methods used in research studies may not reflect those employed in everyday practice. One technique frequently used in clinical practice is screening by identification of clue cells alone. There are no studies of BV treatment that have looked at the effectiveness of treatment in women who have been identified as having BV by this criterion alone. Third, we defined patients as asymptomatic if they were most likely identified through routine prenatal care and were not presenting for evaluation of BV symptoms. However, the details for identification of patients were not explicitly stated in two studies (36,37). Consequently, it is possible that women presenting for evaluation of BV symptoms were also included. The women with symptomatic BV may represent a different risk category for adverse pregnancy outcomes.

Recommendations for Future Research

Further characterization of the population most likely to benefit, if any, is needed. In addition, the optimum timing of screening and treatment to determine the effect of treatment regimens on pregnancy outcomes needs investigation. Particular attention should be paid to the potential adverse effects of treating BV in pregnancy.

Because epidemiologic studies typically use the Gram stain as the diagnostic standard and clinicians typically use clinical criteria, translation of findings from research to clinical practice is of special concern. The development of screening and diagnostic tests that can be used in both research and clinical settings should be a high priority. Published trials are heterogeneous in study size, setting, population, demographics, risk factor assessment, screening methods, and treatment protocols, leading to further concerns about the generalizability of published evidence to clinical practice. Studies that use standard diagnostic criteria and treatment protocols in typical practice settings should be conducted, perhaps using networks of clinical practices. Finally, the timing of screening and treatment needs to be more thoroughly studied, given current evidence suggesting that early screening and treatment may be more effective than late.

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This study was conducted by the Oregon Health Sciences University Evidence-based Practice Center under contract to the Agency for Healthcare Research and Quality (Contract No. 290-97-0018), Rockville, MD.

This article is based on a more comprehensive Systematic Evidence Review which is available online at That document was reviewed by content experts, including Sharon Hillier, Ph.D., University of Pittsburgh, Mark Klebanoff, M.D., M.P.H., National Institute of Child Health & Human Development, National Institutes of Health, and Rick Sweet, M.D., University of Pittsburgh; by professional organizations, including the American Academy of Family Physicians, the American College of Obstetricians and Gynecologists, and the American College of Physicians/American Society of Internal Medicine; and public health organizations, including the Canadian Task Force on Preventive Health Care; the National Institute of Child Health & Human Development; the National Institutes of Health; the Centers for Disease Control and Prevention; and the U.S. Navy Bureau of Medicine and Surgery. Review by these individuals and groups does not necessarily imply endorsement of this article or of the accompanying recommendations of the U.S. Preventive Services Task Force.

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References and Notes

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Author Affiliations

[a]Guise: Department of Obstetrics and Gynecology, Portland, OR.
[b]Guise, Mahon, Helfand: Division of Medical Informatics and Outcomes Research, and Evidence-based Practice Center, Oregon Health Sciences University, Portland, OR.
[c]Aickin: Kaiser Permanente Center for Health Research, Portland, OR.
[d]Helfand: Division of General Internal Medicine, Portland Veterans Affairs Medical Center, Portland, OR.
[e]Peipert: Women and Infants' Hospital of Rhode Island, Providence, RI.
[f]Westhoff: Columbia University College of Physicians and Surgeons, New York, NY.

Copyright and Source Information

This document is in the public domain within the United States as stated in AHRQ's license agreement with the American Journal of Preventive Medicine. For information on reprinting, contact Randie Siegel, Director, Division of Printing and Electronic Publishing, Agency for Healthcare Research and Quality, Suite 501, 2101 East Jefferson Street, Rockville, MD 20852. Requests for linking or to incorporate content in electronic resources should be sent to:

Source: Guise J-M, Mahon SM, Aickin M, Helfand M, Peipert JF, Westhoff C. Screening for bacterial vaginosis in pregnancy. Am J Prev Med 2001:20 (3S):62-72 (

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