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by the American Institute of Ultrasound in Medicine J Ultrasound Med 21:727-729 • 0278-4297 The Microbiological Effects of Endovaginal Sonographic Assessment of Cervical LengthDepartment of Obstetrics and Gynecology, Section of Maternal-Fetal Medicine, The Reading Hospital and Medical Center, West Reading, Pennsylvania. Address correspondence and reprint requests to A. George Neubert, MD, The Reading Hospital and Medical Center, Sixth Avenue and Spruce Street, West Reading, PA 19611.
Objective. To determine whether performance of endovaginal sonography for the measurement of cervical length results in a statistically significant change in endocervical culture results. Methods. Women attending a routine prenatal clinic were offered enrollment in the study. Exclusion criteria included the presence of a cervical cerclage, vaginal examination or coitus within the preceding 24 hours, antibiotic therapy within the preceding 7 days, or the presence of ruptured membranes. A sterile speculum examination and collection of cervical cultures were performed before (initial) and immediately after (final) endovaginal sonographic measurement of cervical length. Quantitative cultures were completed and evaluated for differences in growth by a standardized 4-quadrant technique. Results. A total of 25 women enrolled and completed the study protocol. Quantitative assessment of colony growth showed that the mean growth in the initial samples ± SD was 3.48 ± 1.74, with 1+ indicating growth in 1 quadrant; 2+, growth in the first and second quadrants; 3+, growth in the first, second, and third quadrants; and 4+, growth in all quadrants. The mean growth cultured in the final sample was 3.79 ± 2.26 (P = .364; 95% confidence interval of the difference, –1.00 to +.381). Conclusions. The results of this study do not show a statistically significant inoculation effect associated with performance of endovaginal sonography for the measurement of cervical length.
Key Words: cervical cultures • cervical length • endovaginal sonography • preterm premature rupture of membranes
The use of endovaginal sonography for assessment of the cervix has become increasingly important in the practice of obstetrics. Iams et al1 has reported on the association between the length of the cervix and the risk of spontaneous premature delivery. Digital examination of the cervix remains an equally important adjunct to cervical assessment. In the setting of preterm premature rupture of the membranes, digital examination of the cervix has been shown to decrease the amount of time from rupture of the membranes to the onset of labor (latency period).2 Imseis et al3 studied the microbiological effects of digital cervical examination and found that by performance of a single digital cervical examination, a statistically significant difference in preexamination and postexamination endocervical cultures was obtained. This change in cervical flora may contribute to the development of an intrauterine infection that ultimately leads to premature delivery. When compared with digital examination of the cervix, performance of endovaginal sonographic measurement of cervical length would appear to result in less direct inoculation of the cervix. We questioned whether the inherent differences in technique between digital examination and endovaginal sonographic assessment of the cervix would yield results different from those obtained by Imseis et al.3
Women attending a routine prenatal clinic between 24 and 34 weeks' estimated gestational age were offered enrollment. Gestational dating was based on the recalled last menstrual period or early sonographic dating criteria. The study protocol was approved by our Institutional Review Board before patient enrollment. Informed consent for participation was obtained before the study protocol was begun in all cases. Exclusion criteria included the presence of a cervical cerclage, vaginal examination or coitus within the preceding 24 hours, antibiotic therapy within the preceding 7 days, or the presence of ruptured membranes. The absence of preterm premature rupture of membranes was confirmed by history and the absence of a vaginal pool before completion of the study protocol. A single examiner (J.K.-J.) performed the entire study protocol in all cases. A sterile speculum was placed in the vagina with adequate visualization of the cervix. Specimens for aerobic and anaerobic culture were then obtained in a standard fashion by gentle swabbing of the distal portion of the cervical canal with a Dacron-tipped applicator (Allegiance Healthcare Corporation, McGaw Park, IL). The cultures were labeled as initial and submitted for microbiological study. A standard endovaginal sonographic examination of cervical length, as described by Iams et al,1 was then performed with the use of a nonsterile probe cover and bacteriostatic lubricant (Surgilube; E. Fougera & Co, Melville, NY). The sonographic examination was typically completed in 3 to 5 minutes. On completion of the endovaginal sonographic examination, the probe was withdrawn, and a second sterile speculum examination was immediately conducted with collection of final cultures in a manner identical to that described previously. On arrival in the microbiology laboratory, the swabs were plated by standard methods. Culture material included colistin and naladixic acid, eosin and methylene blue, and chocolate agar. The plates were then incubated under aerobic and anaerobic conditions for 72 and 48 hours, respectively. After incubation, the culture plates were opened and read, with growth being characterized in a semiqualitative manner according to colony morphologic features. Laboratory personnel were not blinded to the order of the cultures. The growth was also categorized in a quantitative manner, with 1+ indicating growth in 1 quadrant; 2+, growth in the first and second quadrants; 3+, growth in the first, second, and third quadrants; and 4+, growth in all quadrants. Those cultures showing limited growth in the first quadrant were characterized as having few colonies (0.5) or 1 colony (0.25) present. The observed amount of growth was assigned a corresponding numeric value to allow for quantitative comparison. A paired 2-tailed t test was then used to compare the mean differences between initial and final culture results. P < .05 was considered significant.
A total of 25 women enrolled and completed the study protocol. The mean age ± SD of the study population was 24.2 ± 6.8 years (range, 16–35 years). Mean gravidity was 2.8 ± 1.5 (range, 1–6), and mean parity was 1.3 ± 1.1 (range, 0–3). The mean estimated gestational age at the time of the study was 29.1 ± 3.1 weeks (range, 24–34 weeks).
Table 1
Among the initial aerobic culture results, Lactobacillus was the most frequent isolate, with Candida species being the next most common. Staphylococcus species, Gardnerella vaginalis, Streptococcus species, group B Streptococcus, Coryneform bacillus, and Enterococcus species completed the list of isolated organisms with the observed percentages.
Quantitative culture results showing mean differences between the initial and final cultures are listed in Table 2
Preterm labor and delivery as a common complication of pregnancy is responsible for considerable perinatal morbidity and mortality. The use of endovaginal sonographic measurement of cervical length is emerging as an important tool in the assessment of risk for preterm labor and delivery. To our knowledge, unlike in digital examination of the cervix, the possibility that performance of endovaginal examinations may result in the introduction of vaginal flora into the cervix has not been studied. Knowledge of the presence or absence of an inoculating effect may alter the frequency or conditions under which these examinations are performed. Although our study is limited by a relatively small sample size, the lack of a statistically significant difference in the culture results leads us to conclude that performance of endovaginal sonography for measurement of cervical length does not result in a significant change in cervical flora as studied. Our results differ from those of Imseis et al,3 in which a similar study protocol did find a statistically significant difference in culture results after a single digital examination of the cervix. We think that the difference in our findings is the result of endovaginal ultrasonic probe placement in the anterior vaginal fornix instead of the endocervical canal, as is the case with digital cervical examination. This fundamental difference results in less direct inoculation of the cervical canal. Additional studies using endovaginal sonography are indicated in a population with preterm premature rupture of the membranes because of concerns for increased rates of infection and a negative effect on the latency period. The apparent absence of an appreciable inoculation effect suggests that endovaginal sonography may be ethically and appropriately used in future studies, thereby allowing for evaluation of this imaging modality in the clinical care of such patients.
Received February 5, 2002, from the Department of Obstetrics and Gynecology, Section of Maternal-Fetal Medicine, The Reading Hospital and Medical Center, West Reading, Pennsylvania.
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Abstract
Introduction