Bacterial Vaginosis in Pregnant Persons to Prevent Preterm Delivery: Screening--Pregnant persons not at increased risk for preterm delivery


Grade: D

Specific Recommendations

The USPSTF recommends against screening for bacterial vaginosis (BV) in pregnant persons who are not at increased risk for preterm delivery.

Frequency of Service

No information available.

Risk Factor Information

Assess risk for preterm delivery. There are multiple factors that increase risk for preterm delivery; one of the strongest risk factors is prior preterm delivery. Decide whether or not to screen for bacterial vaginosis: a. Do not screen pregnant persons who are not at increased risk for preterm delivery. b. Evidence is insufficient to recommend for or against screening pregnant persons at increased risk for preterm delivery.



Practice Considerations

Patient Population Under Consideration

This recommendation statement applies to pregnant persons without symptoms of bacterial vaginosis.


Healthy vaginal flora is comprised of more than 90% lactobacilli. Bacterial vaginosis occurs when there is a shift in this flora to include a greater proportion of mixed anaerobic bacteria, such as the Gardnerella, Prevotella, and Atopobium species.12,13 Most often, bacterial vaginosis is asymptomatic. When symptoms occur, they include off-white, thin, homogenous discharge, a vaginal “fishy” odor, or both.

Assessment of Risk

Persons who are not at increased risk for preterm delivery include pregnant persons with no history of previous preterm delivery or other risk factors for preterm delivery. While multiple factors increase risk for preterm delivery, one of the strongest risk factors is prior preterm delivery. See the Potential Preventable Burden section for additional information on risk factors for preterm delivery.

Screening Tests

Screening tests for bacterial vaginosis are performed on vaginal secretions obtained during a pelvic examination in a primary care setting. Available screening tests include nucleic acid assays, sialidase assays, and clinical assessment (ie, using the Amsel criteria of pH, vaginal discharge, clue cells, and “whiff test”).


Oral metronidazole and oral clindamycin, as well as vaginal metronidazole gel or clindamycin cream, are the usual treatments for symptomatic bacterial vaginosis. The optimal treatment regimen for pregnant persons with bacterial vaginosis is unclear.

Additional Tools and Resources

The Centers for Disease Control and Prevention website provides current treatment recommendations.14

Suggestions for Practice Regarding the I Statement

Potential Preventable Burden

Bacterial vaginosis occurs in as many as 29% of women in the US15 and in 5.8% to 19.3% of pregnant women, depending on the specific population being studied.1,16 Reported factors that increase the likelihood of a diagnosis of bacterial vaginosis include African American race, poverty, smoking, increased body mass index, vaginal douching, low educational attainment, and certain sexual behaviors, including a high number of partners, lack of condom or contraceptive use, vaginal sex, sex with a female partner, and concurrent sexually transmitted infections.6,15,17,18 Causes of preterm delivery are likely multifactorial, and numerous risk factors are associated with an increased risk for preterm birth.6 History of a prior preterm delivery is associated with a 2.5-fold higher odds for preterm delivery in subsequent pregnancies.19 While bacterial vaginosis during pregnancy is associated with a 2-fold higher odds for preterm delivery,2 it is not clear that bacterial vaginosis is a cause of preterm delivery. Other additional risk factors for preterm delivery include, but are not limited to, cervical insufficiency, multifetal gestation, young or advanced maternal age, low maternal body mass index (<20, calculated as weight in kilograms divided by height in meters squared), genitourinary infections, HIV infection, and other maternal medical conditions.6,20-23 The association of these additional risk factors with preterm delivery is small to moderate, and factors can act in isolation or in combination. Preterm birth rates also vary by race/ethnicity in the US; recent data report preterm birth rates of 8.6% among Asian women, 11.8% among Native Hawaiian/Other Pacific Islander women, 9.7% among Hispanic women, 11.5% among American Indian/Alaska Native women, 14.1% among black women, and 9.1% among white women.7 Among women with a prior preterm delivery, the rate of recurrent preterm delivery in African American women is 4 times higher than the rate of recurrent preterm delivery in white women.20 Even when these risk factors are present, it is unclear whether screening and treating asymptomatic bacterial vaginosis in pregnant persons at increased risk for preterm delivery prevents preterm delivery. African American race is both associated with bacterial vaginosis and strongly associated with preterm delivery. Other factors associated with both bacterial vaginosis and preterm delivery include young age, nulliparity, current tobacco use, low educational attainment, lower income, and concurrent sexually transmitted infections. Five studies provided evidence on the benefit of treatment of bacterial vaginosis in women with a previous preterm delivery for reducing the incidence of preterm delivery. Four of these studies evaluated the treatment of bacterial vaginosis with oral metronidazole6 and reported the incidence of preterm delivery at less than 37 weeks. Three of these studies reported statistically significant absolute reductions in preterm delivery after treatment (ranging from 18% to 29% absolute reductions in risk), and 1 study reported no significant difference. Limitations of the evidence, including imprecision, the fact that some of the results were from subgroup analyses, and the inconsistency of results, prevented a definitive conclusion about the benefit.6 Two studies (1 evaluating oral metronidazole and the other evaluating vaginal clindamycin) presented results for preterm delivery at less than 34 weeks, and the results were mixed.6

Potential Harms

The harms of screening for bacterial vaginosis in pregnant persons and treatment with antibiotics generally involve adverse effects such as gastrointestinal upset and vaginal candidiasis.6 Four observational studies and 2 large meta-analyses of observational studies on the use of metronidazole during pregnancy for any reason (not limited to bacterial vaginosis) reported no increase in congenital malformations or incident cancer in children exposed in utero.24-29

Current Practice

No data are available on how frequently pregnant persons at increased risk for preterm delivery are screened for bacterial vaginosis during pregnancy, but screening in asymptomatic pregnant persons is not recommended by any large US professional organization. Clinicians routinely test and treat pregnant persons for symptomatic bacterial vaginosis. Update of Previous USPSTF Recommendation The USPSTF last issued a recommendation on this topic in 2008. Although newer evidence was reviewed, the recommendations have essentially remained the same. The language used to describe a pregnant person’s risk for preterm delivery has been updated to be more consistent with other current USPSTF recommendations.


Assessment Importance Bacterial vaginosis is common and is caused by a disruption of the microbiological environment in the lower genital tract. In the US, reported prevalence of bacterial vaginosis among pregnant women ranges from 5.8% to 19.3% and is higher in some races/ethnicities.1 Bacterial vaginosis during pregnancy has been associated with adverse obstetrical outcomes including preterm delivery,2 early miscarriage,3 postpartum endometritis,4 and low birth weight.5 Bacterial vaginosis is often asymptomatic, can resolve spontaneously, and recurs often, with or without treatment.6 Most clinicians treat symptomatic bacterial vaginosis in pregnancy. The current recommendation statement focuses on screening for asymptomatic bacterial vaginosis in pregnancy. In the US, approximately 10% of live births are preterm (born prior to 37 weeks’ gestation).7 Preterm birth is associated with serious complications, including major intraventricular hemorrhage, acute respiratory illnesses, and sepsis.7-10 Approximately two-thirds of all infant deaths in the US occur among infants born preterm.8 The frequency and severity of adverse outcomes from preterm delivery are higher with earlier gestational age. Magnitude of Net Benefit The US Preventive Services Task Force (USPSTF) concludes with moderate certainty that screening for asymptomatic bacterial vaginosis in pregnant persons not at increased risk for preterm delivery has no net benefit in preventing preterm delivery. The USPSTF concludes that for pregnant persons at increased risk for preterm delivery, the evidence is insufficient and conflicting, and the balance of benefits and harms cannot be determined. See the Table for more information on the USPSTF recommendation rationale and assessment. For more details on the methods the USPSTF uses to determine the net benefit, see the USPSTF Procedure Manual.11


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