Updated recommendations from the U.S. Preventive Services Task Force advise against screening for bacterial vaginosis in pregnant women who are asymptomatic and at low risk for preterm delivery.
But the recommendations remain neutral about screening in high-risk pregnancies because “current evidence is insufficient to assess the balance of benefits and harms,” said Dr. Ned Calonge, chair of the U.S. Preventive Services Task Force (USPSTF) and colleagues.
The new recommendations (Ann. Intern. Med. 2008;148:214-9) are an update of those compiled by the task force in 2001 (Am. J. Prev. Med. 2001;20:59-61). They are based on an analysis of new evidence, conducted for the task force by Peggy Nygren of the Oregon Health and Science University, Portland, and her associates and funded by the Agency for Healthcare Research and Quality (Ann. Intern. Med. 2008;148:220-33).
The analysis addressed “previously identified gaps, such as the characterization of patients most likely to benefit from screening and the optimal timing of screening and treatment in pregnancy outcomes,” said Dr. Calonge, who is also chief medical officer of the Colorado Department of Public Health and Environment, Denver, and his colleagues.
Ms. Nygren and her associates noted the recent concerns that metronidazole, the antibiotic most commonly used to treat bacterial vaginosis, might increase preterm births in some populations. “The juxtaposition of these data, along with epidemiologic evidence associating bacterial vaginosis with preterm birth, leads to considerable confusion for clinicians and researchers alike. Whether to screen or treat multiple times, when to start, and at what interval during pregnancy are unanswered questions, as bacterial vaginosis may not necessarily persist throughout pregnancy,” they wrote.
The analysis included studies published after the release of the task force's 2001 recommendations to examine “new evidence on … screening and treating bacterial vaginosis in asymptomatic pregnant women.”
Asymptomatic patients were defined as those presenting for routine prenatal care and not for evaluation of vaginal discharge, odor, or itching. Low-risk patients were defined as having no history of and no risk factors for preterm delivery, whereas average-risk patients were defined as “the general population,” regardless of risk status. Women with a history of preterm delivery related to spontaneous rupture of membranes or spontaneous preterm labor were categorized as high risk.
The analysis found no benefit in treating women with low- or average-risk pregnancies if they were asymptomatic. For high-risk asymptomatic pregnancies, Ms. Nygren and her colleagues noted that findings from one trial that had been published since the USPSTF 2001 recommendations showed “a significant adverse effect of treatment on delivery before 37 weeks” in 127 women, “indicating that treatment of bacterial vaginosis increased the chance of preterm delivery” significantly (S. Afr. Med. J. 2002;92:231-4).
However, when this study was considered with previous studies that had been included in the 2001 recommendations, the results were “heterogenous and conflicting,” they wrote. For the outcome of delivery before 37 weeks, three of the trials reported a significant treatment benefit, one showed significant treatment harm, and one showed no benefit. “Inherent differences in populations, such as previous pregnancy complications, gestational age, ethnicity, or co-infection, may also influence which women are helped or harmed by screening and treatment for bacterial vaginosis,” they wrote, noting “a potential but unclear benefit of treatment for some [high-risk] patients.”
In keeping with the USPSTF recommendation against screening in low-risk pregnancies, the Centers for Disease Control and Prevention (CDC), the American Academy of Family Physicians (AAFP), the American College of Obstetricians and Gynecologists (ACOG), the Cochrane Pregnancy and Childbirth Group, the British Association for Sexual Health and HIV/Clinical Effectiveness Group (BASHH) have similar recommendations.
Although the task force maintains its neutral position regarding high-risk pregnancies, the CDC, ACOG, AAFP and BASHH say there might be high-risk women for whom screening and treatment may be beneficial, the USPSTF authors wrote, noting that optimal treatment for bacterial vaginosis in pregnancy remains unclear.