During the first prenatal visit, patients from both groups were managed the same: symptoms of preterm labor (regular uterine contractions) and vaginal infection (discharge, burning, itching, and odor) were investigated and recorded as present or absent. The following laboratory tests were performed: vaginal pH, wet mount, dieoxyribonucleic acid (DNA) probe for C trachomatis and N gonorrhoeae, and urinalysis.
At each subsequent prenatal visit, women from both groups were asked about symptoms of preterm labor, vaginal infection, and urinary tract infection. Women in either group who reported symptoms of preterm labor had a wet mount examination, DNA probe, and urinalysis performed; women with vaginal symptoms had a wet mount and DNA probe performed. Experimental and control group subjects differed in that experimental group members had a vaginal pH level tested by their physician at each prenatal visit (controls did not have pH testing after the initial visit), and women with a pH level >4.5 also had a wet mount examination performed. The vaginal pH level was tested using a strip of specially formulated pH paper with an enhanced range in the spectrum of interest (pH = 4.0 to 5.5; paper manufactured by Micro Essential Laboratory, Brooklyn, NY). Participating study physicians were instructed in the technique for determining vaginal pH levels. The patient’s physician recorded the pH value in the medical record.
For the purposes of our study, a wet mount evaluation by a medical technologist was used to diagnose bacterial vaginosis, trichomoniasis, and vulvovaginal candidiasis. Participating medical technologists were formally trained in laboratory procedures and were required to have proficiency testing on wet mount examinations 3 times a year. The medical technologists were blinded to participants’ group assignments. Our selection of the wet mount examination as the confirmatory diagnostic test for vaginal infections was made on the basis of its applicability to each of the 3 types of infection, its utility for private practice (relatively easy to perform and inexpensive), and on previous data reporting its relatively high sensitivity for the diagnosis of G vaginalis, the most prevalent bacteria in bacterial vaginosis. The sensitivity of the wet mount for detecting G vaginalis and T vaginalis is 90% and 100%, respectively, when synthetic oligonucleotide probes are used as a gold standard.16 Other researchers have also used medical technologists’ readings of wet mounts as a standard for the diagnosis of bacterial vaginosis.17
Women from both experimental and control groups who were diagnosed with a specific vaginal or cervical infection were given standard antimicrobial treatments specified in the study protocol. Although most women diagnosed with bacterial vaginosis or trichomoniasis received oral antibiotics (metronidazole 500 mg twice daily for 7 days or clindamycin 300 mg twice daily for 7 days), a minority were treated with vaginal antimicrobials.
Hospital charts were also reviewed for gestational age at the time of delivery. Gestational age was determined using clinical parameters with ultrasound confirmation for cases where clinical dates were uncertain. Women who delivered at 20 weeks’ to less than 37 weeks’ gestation were categorized as having had a preterm delivery, consistent with accepted definitions.18
We used the chi-square test to look for significant differences between the 2 groups in infection, antibiotic treatment, and preterm delivery rates. The sensitivity and specificity of vaginal pH values and symptom reports for detecting bacterial vaginosis and T vaginalis were determined using data from the initial prenatal visits, where both vaginal pH and wet mount examinations were routinely performed.
Results
We invited a total of 243 women to participate in our study. Not all eligible patients who were pregnant at the time of the study were asked to participate because of staff changes and work demands. One hundred one declined to participate because of a reluctance to undergo routine vaginal examinations. Twenty-one additional women initially expressed interest in the study, but subsequently transferred care or had a spontaneous or induced abortion before their first formal prenatal visit. The 121 women randomized into our study (63 women in the experimental group; 58 in the control group) represented an overall response rate of 50% (number of participants divided by number of women invited to participate). Two women were pregnant twice during the course of the study, resulting in 123 total pregnancies. There were 910 prenatal visits during the course of the study, with an average of 7.4 prenatal visits per pregnancy. When our study population was compared with nonparticipating obstetrical patients at the 3 clinic sites, no differences were seen in age and proportion of women insured by public assistance. However, compared with nonparticipants, the study sample included a higher proportion of whites.