Putting Prevention into Practice

An Evidence-Based Approach

Screening for Bacterial Vaginosis in Pregnancy to Prevent Preterm Delivery

Am Fam Physician. 2009 Apr 15;79(8):697-698.

This clinical content conforms to AAFP criteria for evidence-based continuing medical education (EB CME). See CME Quiz on page 645.

Case Study

E.R., a 23-year-old Mexican-American woman, presents for her first prenatal visit after a positive home pregnancy test. Her last menstrual cycle was 12 weeks ago. E.R.'s medical history includes outpatient treatment for an episode of pelvic inflammatory disease. She has a two-year-old child who was born at 34 weeks' gestation. Her physical examination is normal.

Case Study Questions

1. Which one of the following approaches would be most consistent with the U.S. Preventive Services Task Force (USPSTF) recommendation on screening for bacterial vaginosis?

  • A. Do not screen E.R. for bacterial vaginosis because the harms of screening pregnant women outweigh the benefits.

  • B. Screen E.R. for bacterial vaginosis because she is at high risk of preterm delivery.

  • C. Screen E.R. for bacterial vaginosis because all pregnant women should be screened routinely.

  • D. Explain to E.R. that testing for bacterial vaginosis is an option because of her high risk of preterm delivery, but that the evidence is insufficient to recommend routine screening.

2. If E.R. had a vaginal discharge, which one of the following findings or combinations of findings would fulfill the Amsel criteria for diagnosis of bacterial vaginosis?

  • A. Vaginal pH less than 4.7 and clue cells on wet mount.

  • B. Vaginal pH greater than 4.7 and “fishy odor” when potassium hydroxide is added to discharge.

  • C. Clue cells on wet mount, with no other findings.

  • D. “Fishy odor” when potassium hydroxide is added to discharge, with no other findings.

3. Which of the following patients is/are considered to be at increased risk of preterm delivery?

  • A. A 25-year-old black woman who is an attorney.

  • B. A 25-year-old unemployed white woman receiving welfare benefits.

  • C. A 25-year-old Hispanic woman whose first child was born at 32 weeks' gestation.

  • D. A 25-year-old Asian woman with a history of pelvic inflammatory disease.

Answers

1. The correct answer is D. Testing for bacterial vaginosis is an option because of E.R.'s high risk of preterm delivery; however, the evidence is insufficient to recommend routine screening. The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening for bacterial vaginosis in asymptomatic pregnant women at high risk of preterm delivery.

Bacterial vaginosis is the most common lower genital tract syndrome in women of reproductive age. Symptoms can include vaginal discharge, pruritus, or malodor. Up to 50 percent of cases of bacterial vaginosis resolve spontaneously during pregnancy. However, the presence of bacterial vaginosis has been associated with adverse pregnancy outcomes, including preterm delivery.

The USPSTF recommends against screening for bacterial vaginosis in asymptomatic pregnant women at low risk of preterm delivery. No direct evidence indicates that screening for bacterial vaginosis reduces adverse health outcomes for these women. Good evidence indicates that treatment of bacterial vaginosis in these women lacks benefit.

2. The correct answer is B. The Amsel criteria for the clinical diagnosis of bacterial vaginosis require at least three of the following: vaginal pH greater than 4.7; clue cells on wet mount; the presence of a thin, homogenous discharge; and an amine “fishy odor” when potassium hydroxide is added to the discharge. A positive Gram stain is considered the criterion standard for diagnosis but is often impractical to perform in primary care settings.

3. The correct answers are A, C, and D. Patients considered to be at increased risk of preterm delivery are black women, women with a history of a pelvic infection, and women with a previous preterm delivery. Women of low socioeconomic status are at increased risk of developing bacterial vaginosis, but are not considered to be at increased risk of preterm delivery.

SOURCES

U. S. Preventive Services Task Force. Screening for bacterial vaginosis in pregnancy to prevent preterm delivery: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med. 2008;148(3):214–219.

Nygren P, Fu R, Freeman M, Bougatsos C, Klebanoff M, Guise JM. Evidence on the benefits and harms of screening and treating pregnant women who are asymptomatic for bacterial vaginosis: an update review for the U.S. Preventive Services Task Force. Ann Intern Med. 2008;148(3):220–233.

The case study and answers to the following questions on screening for bacterial vaginosis in pregnancy to prevent preterm delivery are based on the recommendations of the U.S. Preventive Services Task Force (USPSTF), an independent panel of experts in primary care and prevention that systematically reviews the evidence of effectiveness and develops recommendations for clinical preventive services. More detailed information on this subject is available in the USPSTF Recommendation Statement and the evidence synthesis on the USPSTF Web site (http://www.ahrq.gov/clinic/uspstfix.htm). The evidence synthesis and Recommendation Statement are available in print through the AHRQ Publications Clearinghouse (800-358-9295, e-mail, ahrqpubs@ahrq.hhs.gov). The practice recommendations in this activity are available at http://www.ahrq.gov/clinic/uspstf/bvag.htm.


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