BACKGROUND: Bacterial vaginosis has recently been associated with preterm labor and delivery. The purpose of our study was to determine whether regular prenatal vaginal pH testing resulted in more frequent diagnoses of bacterial vaginosis and other vaginal infections, more frequent treatment with antibiotics, and fewer preterm deliveries. We also sought to determine the sensitivity and specificity of pH testing and vaginal symptom reporting in identifying vaginal infections.
METHODS: Our study was a prospective clinical trial involving 121 pregnant women randomized to receive either standard prenatal care, including routine inquiry about vaginal symptoms, or standard care supplemented by vaginal pH testing. Women with symptoms or a vaginal pH level >4.5 received a wet mount examination. Confirmed infections were treated according to study protocols.
RESULTS: Women who received regular pH testing showed significantly higher detection rates for bacterial vaginosis than controls (48.4% vs 27.1%, P =.015) and more frequent detection of Trichomonas vaginalis (7.8% vs 1.7%, P = .116). A higher percentage of women in the experimental group were treated for bacterial vaginosis and trichomoniasis (46.9% vs 27.1%, P =.024), and the preterm birth rate was one half that of the control group (4.7% vs 10.2%, P = .243). The presence of vaginal symptoms or a vaginal pH level >4.5 identified bacterial vaginosis or trichomoniasis with 84.4% sensitivity.
CONCLUSIONS: In our study, frequent vaginal pH testing during pregnancy resulted in more frequent diagnosis and treatment of bacterial vaginosis. Since vaginal symptoms and elevated pH levels appear to be useful in screening for bacterial vaginosis and trichomoniasis, frequent pH testing should be evaluated in larger studies.
Preterm delivery is one of the most important—and most costly—problems in obstetric medicine. Despite recent advances, nearly 10% of all infants in this country are born preterm.1 Advances in the care of premature newborns, such as the administration of antenatal corticosteroids, the use of surfactant, and other developments in respiratory technology have improved outcomes, yet a greater emphasis on identifying and managing the causes of premature delivery is needed.
Recent research has indicated that maternal infection probably plays a much greater role in the occurrence of preterm labor than was previously understood. Bacterial byproducts have been shown to stimulate endogenous phospholipase A2, which induces the formation of prostaglandin, an important stimulant of uterine contractions.2 Further, neutrophils and their constituent enzymes, together with bacteria and their proteases, weaken the amniochorion, predisposing a woman to premature rupture of membranes.3 A study4 comparing placentas from 21 women who delivered before 36 weeks’ gestation with those from 66 women who delivered at term found the rate of infected placentas to be 62% and 12%, respectively.
Specific genital infections have been linked to preterm labor, including sexually transmitted infections secondary to Chlamydia trachomatis, Neisseria gonorrhoeae, and Trichomonas vaginalis.5 Bacterial vaginosis, which is more common and not necessarily sexually transmitted, is associated with a 1.4- to 6.9-fold increased risk of preterm delivery.6-9 The relatively high prevalence of bacterial vaginosis in the obstetric population (10% to 32%),10 coupled with evidence that screening and treating the condition reduces the rate of preterm deliveries,11-13 makes detection important for reducing perinatal morbidity and mortality.
There is scant evidence that can be used to determine the optimal screening regimen for bacterial vaginosis in pregnancy. It is unclear, for example, whether all women should be routinely screened, how often the screening should occur, and which tests should be used. The vaginal pH test may be a valuable screening tool. It is a quick, inexpensive test where values >4.5 indicate the presence of either bacterial vaginosis or trichomoniasis. The sensitivity for detecting bacterial vaginosis with pH testing ranges from 84% to 97%.14 An elevated vaginal pH level has been shown to be 100% sensitive and 92% specific in screening nonpregnant premenopausal women for aerobic bacterial pathogens (b-hemolytic streptococci, Gardnerella vaginalis, or mixed aerobic organisms).15 However, little is known about the utility of the vaginal pH level as a screening tool in pregnancy.
The purpose of our study was to determine whether regular prenatal vaginal pH level screening resulted in more frequent diagnoses and treatment of bacterial vaginosis, trichomoniasis, and other genital infections and thus fewer preterm deliveries. In addition, we sought to determine the effectiveness of using recent vaginal symptoms and vaginal pH levels to diagnose bacterial vaginosis and trichomoniasis.
Methods
We enrolled pregnant women of less than 34 weeks’ gestation attending 1 of 3 participating clinics located in the Minneapolis/St. Paul, Minnesota, metropolitan area between July 1, 1996, and December 31, 1997. We calculated that a sample size of 208 women would detect a 50% increase in the diagnosis of bacterial vaginosis with a power of .80 and an a of .05. Women who participated in the study were randomized into experimental and control groups at the initial prenatal visit, using computer-generated random number tables and sealed envelopes containing the patient’s group assignment and study protocol. A study protocol was placed in the patient’s chart to facilitate group-specific clinical procedures and data collection Table 1; therefore, health care providers and subjects were not blinded to the intervention (vaginal pH testing).