The mean age of the participants was 24.8 years (standard deviation = 5.4), and 60.2% of the women were on public assistance. The population included several ethnic groups: 47.2% were African American; 36.6% white; 4.1% Native American; 3.3% Asian; 1.6% Hispanic; and 7.2% unknown or other. There were no differences between experimental and control groups in age, ethnicity, and proportion of women on public assistance.
Women who underwent regular vaginal pH screening in addition to standard prenatal care showed significantly higher rates for the diagnosis of bacterial vaginosis, more frequent diagnosis of trichomoniasis (not statistically significant), higher antibiotic treatment rates for bacterial vaginosis and trichomoniasis (46.9% vs 27.1%, P = .024), and a lower rate of preterm births (not statistically significant; Table 2.
The sensitivity of a high vaginal pH level or vaginal symptoms in identifying women with bacterial vaginosis or trichomoniasis was 84.4% Table 3. Although the specificity of either of these tests for identifying bacterial vaginosis or trichomoniasis was modest (57.1%), it rose to 78.5% when both a high pH value and vaginal symptoms were present. Of the 27 women were given a diagnosis of and treatment for bacterial vaginosis and had follow-up wet mount evaluations,15 (55.6%) had recurrent or persistent bacterial vaginosis.
Discussion
In our study, regular testing for vaginal pH levels at prenatal examinations resulted in significantly more diagnoses of bacterial vaginosis and more antibiotic prescriptions. Increased recognition and treatment of bacterial vaginosis may have contributed to the reduced number of preterm deliveries seen in the experimental group; however, we did not calculate our sample size using preterm delivery as a primary outcome, and the number of women we recruited fell short of the number required to detect a significant difference in the preterm delivery rate.
Given the randomized design of this study, the 1.8-fold increase in the rate of diagnosis of bacterial vaginosis among experimental subjects compared with controls (48.4% vs 27.1%) was likely a result of the increased screening with vaginal pH testing. It is noteworthy that the prevalence of bacterial vaginosis in the control group (27%) is near the upper end of the 10% to 32% range reported for other previously studied obstetric populations.10 This high-normal rate of infection may be related to the relatively high proportion of women of lower socioeconomic status, a group known to be at risk for preterm labor.19 In addition, our procedure of asking both experimental and control subjects about symptoms of vaginal infection as a routine part of each prenatal visit may have increased the rate of detecting infections for both groups. Given the high-risk nature of our population, it is notable that our controls had a preterm birth rate (10.2%) comparable with that of the general population,1 and the experimental group’s preterm birth rate (4.7%) was less than half that of the controls.
A high vaginal pH value, vaginal symptoms, or both had 84% sensitivity to detect bacterial vaginosis or trichomoniasis. Inquiring about a history of vaginal symptoms and testing for vaginal pH levels are inexpensive procedures that could easily be implemented as part of routine prenatal care. If larger studies confirm its impact on the detection of infection and the preterm delivery rate, vaginal pH testing will merit wide use as a screening tool, with its results confirmed by more specific diagnostic procedures, such as the wet mount or Gram stain.
Nearly half of our sample received antimicrobial prescriptions for vaginal infections. Yet 56% of those treated who also had follow-up wet mount examinations had either persistent or recurrent bacterial vaginosis. This rate is 3 times higher than the 18% recurrence rate previously reported20 and may indicate either noncompliance, resistance to the medication, or a tendency toward recurrence. Women who continue to have evidence of infection may remain at risk for preterm birth. A more effective strategy for eliminating bacterial vaginosis resulting in a lower rate of persistence or recurrence in the experimental group may have improved the preterm labor outcomes for women undergoing regular screening.
Limitations
An important limitation of this study is the relatively small sample size. Although we demonstrated a significant difference in our primary outcome (infection rates), the more compelling clinical outcome is preterm delivery rate. McGregor and colleagues11 demonstrated a 50% reduction in bacterial-vaginosis–linked idiopathic preterm births with a program of screening for and treating bacterial vaginosis.11 To have 80% power to show a reduction in preterm birth from 10% to 5%, we would have needed a sample size of 336 mothers in each group—a number beyond our capacity to fund and recruit.