Effectiveness of Labor Cervical Examination Simulation in Medical Student Education

Original Research Effectiveness of Labor Cervical Examination Simulation in Medical Student Education

Joshua F. Nitsche, MD, PhD, Kristina M. Shumard, MD, Nora F. Fino, MS, Jeffrey M. Denney, MD, MS, Kristen H. Quinn, MD, MS, John C. Bailey, MD, Rubymel Jijon, MD, Chenchen Huang, MD, Kendra Kesty, MD, Paul W. Whitecar, MD, Arnold S. Grandis, MD, PhD, and Brian C. Brost, MD

OBJECTIVE: To estimate whether simulation training RESULTS: Cervical examination students were signifi- improves medical students’ cervical examination accu- cantly more accurate (Mann-Whitney, P,.001) in assess- racy. ing dilation (73% exact, 98% within 1 cm) and effacement BACKGROUND: The training paradigm for the labor (83% and 100%) than vaginal delivery students (dilation cervical examination exposes patients to additional 52% and 82%, effacement 51% and 96%). In the cumu- examinations, lacks a gold standard, and does not lative summation analyses, 65–100% of students attained objectively assess trainee competence. To address these competence during the clerkship depending on the level issues and optimize training, we assessed the effective- of accuracy and cervical parameter assessed. On average, ness of cervical examination simulation in third-year competence was achieved with 27–44 repetitions. medical students. CONCLUSION: Simulation training dramatically METHODS: During the obstetrics and gynecology clerk- improved student accuracy in labor cervical examina- ship, a cohort study was performed in which third-year tions. Because not all students achieved competence, the students were assigned to receive cervical examination cumulative summation analyses suggest that more than simulation (n550) or vaginal delivery simulation (n548), 100 repetitions would be needed if the goal was for the with each group serving as a simulation-naive control for entire class of students to achieve competence. the other skill. As a final assessment, students performed (Obstet Gynecol 2015;126:13S–20S) 10 cervical examinations using task trainers. Exact accu- DOI: 10.1097/AOG.0000000000001027 racy and accuracy within 1 cm were compared between LEVEL OF EVIDENCE: II groups. Cumulative summation analyses were performed on the cervical examination group to assess competence he classic training schema for the labor cervical and the average number of repetitions needed to Texamination involves a trainee examining a woman achieve it. in labor after which an experienced health care provider repeats the examination to determine the accuracy of the From the Division of Maternal Fetal Medicine, Department of Obstetrics–Gynecology, trainee’s assessment. Often there is no objective assess- and the Department of Biostatistical Sciences, Wake Forest School of Medicine, Winston-Salem, North Carolina; and the Division of Maternal Fetal Medicine, ment of the trainee or a predetermined competence Department of Obstetrics–Gynecology, Mayo Clinic College of Medicine, Rochester, level for this skill. The subjective and imprecise nature Minnesota. of the labor cervical examination is clearly evident in Presented at the 2015 Council on Resident Education in Obstetrics and Gyne- the studies that have investigated the performance of cology and the Association of Professors of Gynecology and Obstetrics Annual Meeting, March 4–7, 2015, San Antonio, Texas. this skill. Studies using rigid cervical models have shown accuracy rates of approximately 49%1 and 58%2 and The authors thank Dr. Bennett Gardner and Dr. Linda Street for their assistance 2 with the simulation sessions. intraobserver variability of 52%. Assessment of accu- “ ” Corresponding author: Joshua F. Nitsche, MD, PhD, Wake Forest University racy on more realistic soft cervices made of pillow School of Medicine, Division of Maternal Fetal Medicine, Department of foam has shown an even lower accuracy of only 19%.3 – Obstetrics Gynecology, Medical Center Boulevard, Winston-Salem, NC Based on these assessments of health care pro- 27157; e-mail: [email protected]. Financial Disclosure vider accuracy, there is room for improvement in the The authors did not report any potential conflicts of interest. training of this skill. In addition, the current paradigm is both anxiety-provoking for the trainee and exposes © 2015 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved. the patient to additional cervical examinations, which ISSN: 0029-7844/15 may cause harm. Furthermore, training parameters

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Copyright ª by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. such as the accuracy needed for competence, the best review board and Novant Health’s institutional review frequency and interval of training sessions, or the board. Residents and faculty were surveyed regarding number of repetitions needed to achieve competence the realism and usefulness of the polyvinyl chloride have not been defined nor has an objective way to pipe and silicone cervical examination models. assess trainee skill been devised. Third-year medical students at Wake Forest To address these issues, we have created a 6-week School of Medicine participating in the obstetrics curriculum surrounding a self-constructed cervical and gynecology clerkship were assigned one to one examination training model made from polyvinyl to receive cervical examination or vaginal delivery chloride pipe, soft foam, and nitrile rubber sheets that simulation during the first 5 weeks of the clerkship. allows for a simulated blind cervical examination, Although the simulations were a required part of the similar to the model used by Huhn and Brost3 hypoth- clerkship, the students were allowed to opt out of esizing that simulation would lead to an increase in having their data included in the study without accuracy. We report our assessment of the curricu- affecting their grade. All students received instruction lum’s and model’s effectiveness in third-year medical discussing the basics of the labor cervical examination students participating in the obstetrics and gynecology and vaginal delivery and a 1-hour simulation session clerkship in 2014–2015. on how to perform a labor cervical examination and a 45-minute group simulation (three to four students) MATERIALS AND METHODS on how to perform a vaginal delivery. During the This project used a cervical examination task trainer initial cervical examination session, students mea- similar to the one developed by Dr. Brian Brost.3 A6- sured their fingers to better understand how their in long piece of 4-in diameter polyvinyl chloride pipe finger dimensions can be used to estimate cervical served as a simulated pelvis. Several pillow foam cyl- dilation and effacement. They also examined hard inders of differing consistencies then were covered with cervical models, interchangeable with the soft cervi- thin nitrile or latex rubber (from examination gloves) ces, under direct visualization and blindly inside the to form a vagina, amniotic sac, cervix, and perineal polyvinyl chloride pipes. tissue. Many different cervices were constructed with During the first 5 weeks of the clerkship, students various combinations of dilation (1, 2, 3, 4, 5, 6, or in the cervical examination simulation group partic- 7 cm) and effacement (0.5, 1, 2, 3, or 4 cm long or ipated in five 1-hour sessions using the polyvinyl 100%,75%,50%,25%,0%effaced)toallowthemodel chloride task trainer with soft foam cervices, whereas to reproduce the variability encountered in clinical the vaginal delivery students had four 1-hour sessions practice. After the foam components are placed in using the Noelle birthing simulator. Students assigned the appropriate order, rubber caps were placed over to vaginal delivery training had the typical clerkship each end of the simulated pelvis. Assembly of the experience with the labor cervical examination and model is depicted in Figure 1. Trainees insert their were used as simulation-naive controls for the cervical fingers through a triangular opening in the distal cap, examination group. The number of real-life cervical simulating the pubic arch, through the perineal tissue examinations performed by each student was re- and vagina to perform a blind cervical examination corded and compared with a t test. At the end of week estimating dilation and effacement. Ten task trainers 5, each student examined a set of 10 polyvinyl chlo- were constructed to allow many trainees to use them ride task trainers. After the silicone models were com- simultaneously in one training session. pleted, each student examined a set of 10 polyvinyl Silicone rubber-based cervical examination task chloride task trainers and 10 silicone task trainers dur- trainers, produced by Human Analog Applications, ing the final assessment. Accuracy was compared were also used. These task trainers include an between groups using a Mann-Whitney test. Assess- anatomically correct bony pelvis, realistic-feeling ments of dilation and effacement were analyzed sep- perineal and vaginal tissue, and 30 different cervices arately. Exact accuracy and accuracy within 1 cm of varying combinations of dilation (1, 2, 3, 4, 5, 6, 7, were assessed for both dilation and effacement 8, 9, or 10 cm) and effacement (0.5, 1, 2, 3, or 4 cm because these margins of error have been investigated long or 100%, 75%, 50%, 25%, 0% effaced). Pictures of in other studies.1,2,4 In addition, accuracy within 1 cm the silicone task trainer are provided in Figure 2. Ten is relevant because discerning this amount of cervical models were constructed to allow many trainees to change per hour is necessary to determine if labor has use them simultaneously in one training session. progressed or arrested in nulliparous women. Com- This cohort study was deemed exempt from review parison of student performance between the polyvinyl by the Wake Forest School of Medicine institutional chloride and silicone models was performed using

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Copyright ª by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. Fig. 1. Schematic drawing of polyvinyl chloride (PVC) cervical examination task trainer. Proximal cap (A); amniotic membranes and fetal head (B); cervix (C); vagina (D); PVC pelvis (E); perineum (F); distal cap (G); pubic arch (H). Nitsche. Medical Student Cervical Examination Simulation. Obstet Gynecol 2015. a Mann-Whitney test. In week 6, students received an models using the likelihood ratio test. If the first two additional 1 hour of simulation training in the other models were significantly different, we fit a third skill to which they were originally assigned. Student model that allowed both the intraobserver and inter- performance on a final simulated vaginal delivery was observer variability to vary by training group (model also compared. Given the distinct skills required for 3). The second and third models were similarly com- the two tasks, these data will be submitted in a separate pared using the likelihood ratio test. If the first two report. models were not significantly different, we fit a model To assess the ability of the polyvinyl chloride in which there intraobserver variability varied by models to discriminate between health care providers training group and the interobserver variability was based on experience level, we compared the accuracy homogenous. This model was compared with the of the vaginal delivery students (who performed the original model using the likelihood ratio test. fewest examinations) to obstetrics and gynecology Cumulative summation is a statistical method residents (who perform the most examinations and used in several areas of medicine including obstetrics prior studies indicate are the most accurate2,3) using and gynecology.6–9 In this method, the endpoint must a Mann-Whitney test. be binary, that is success compared with failure, and To assess between-participant (interobserver) and acceptable and unacceptable failure rates are set. within-participant (intraobserver) variability, a statisti- These parameters are used to determine the amount cian (N.F.F.) performed a series of nested linear mixed the cumulative summation score decreases with each models, as described by Hedeker et al.5 These models success and increases with each failure and define used the margin of error of the dilation or effacement competence intervals for the cumulative summation assessment as the outcome and were adjusted for hav- score. An individual’s progress can be tracked by ing had cervical examination training. The random graphing the cumulative summation score against effects reflected the between-participant variability, the number of repetitions with a declining score being whereas the error variance reflected the within- favorable and an increasing one unfavorable. Compe- participant variability. We began by fitting a model tence is achieved when the score decreases past a pre- with a common random intercept and error variance. defined number of threshold intervals. In this model, the intraobserver and interobserver The data from the cervical examination students variability is considered homogenous in the trained were subjected to a series of cumulative summation and untrained groups (model 1). We then fit a model analyses (considering dilation and effacement sepa- in which the interobserver variability varied by train- rately). In the first set of analyses, success was defined ing group but the intraobserver variability remained as an exactly correct estimation. A study in which a very homogenous (model 2) and compared these first two experienced physician verified more junior physicians’

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Copyright ª by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. Fig. 2. Silicone cervical examination task trainer. A. Front view of the completely assembled task trainer with realistic external genitalia. B. Rear view of task trainer with vagina and cervix insert (C and D) and fetal head (E) removed, showing anatomically correct pelvic structures. C. Combined vagina and cervix insert viewed from within the uterus looking through the cervix into the vagina. D. Lateral view of the vagina and cervix insert with the vagina on the right and cervix on the left. E. Back of trainer with fetal head insert attached. F. Speculum examination view of the task trainer showing the cervix with fetal head insert (E) seen through the cervical os. Nitsche. Medical Student Cervical Examination Simulation. Obstet Gy- necol 2015. examinations found agreement only 49% of the time.4 medical students were assigned to either cervical exam- As the distractions of labor and delivery are removed ination (n550) or vaginal delivery training (n548) with from simulation, we set the acceptable and unacceptable none opting out of the study. There were 27 male and failurerateslightlyhigherat25%(75%correct)and 23 female cervical examination students and 32 male 50%, respectively. In the second set of cumulative sum- and 16 female vaginal delivery students with no signif- mation analyses, success was defined as an estimate icant differences between groups (x2, P..05). Cervical within 1 cm of the actual value and set the acceptable examination and vaginal delivery students performed and unacceptable failure rates at 10% and 25%, respec- an average of 2.561.8 and 1.661.5 cervical examina- tively. Because sustained accuracy is required for appro- tions, respectively, during the clerkship (P5.02). On priate management of labor, the students were average, the students who received cervical examina- designated competent if their cumulative summation tion training performed 76617 simulated examinations score decreased past two threshold intervals. (range 40–100), depending on the number of sessions missed as a result of other clinical responsibilities. Re- RESULTS sults of the final assessment using the polyvinyl The results of the resident and attending surveys chloride models are provided in Table 2. For both (n520) are included in Table 1. Ninety-eight third-year dilation and effacement, the estimates of the cervical

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Survey Item Value

How would you rate the overall realism of the silicone cervical examination model? 3.661.1 Poor (1) Fair (2) Good (3) Very Good (4) Excellent (5)

Repetitive use of the silicone cervical examination model will improve an inexperienced health care provider’s 4.161.0 clinical skill with cervical examinations. Strongly Disagree (1) Disagree (2) Neutral (3) Agree (4) Strongly Agree (5)

In your opinion, the usefulness of the silicone cervical examination model in medical student and resident education 4.061.4 will be: Poor (1) Fair (2) Good (3) Very Good (4) Excellent (5)

How would you rate the overall realism of the polyvinyl chloride pipe cervical examination model? 2.860.5 Poor (1) Fair (2) Good (3) Very Good (4) Excellent (5)

Repetitive use of the polyvinyl chloride pipe cervical examination model will improve an inexperienced health care 4.160.4 provider’s clinical skill with cervical examinations. Strongly Disagree (1) Disagree (2) Neutral (3) Agree (4) Strongly Agree (5)

In your opinion, the usefulness of the polyvinyl chloride pipe cervical examination model in medical student and 3.760.8 resident education will be: Poor (1) Fair (2) Good (3) Very Good (4) Excellent (5)

Which model was the most realistic? Polyvinyl chloride pipe 15 Silicone 85

Which model would be more useful in the cervical examination training of medical students and residents? Polyvinyl chloride pipe 20 Silicone 80 Data are mean score6standard deviation or % of respondents. examination students were exactly correct and within 1 There was no difference in the accuracy of assess- cm, significantly more often than the students who ments within 1 cm. Students from both groups were received vaginal delivery simulation. more accurate when examining the polyvinyl chloride The silicone models were used in the assessments pipe compared with the silicone models (Table 4). of 30 cervical examination and 27 vaginal delivery Theresultsfromthecomparisonofvarianceare students (Table 3). For dilation and effacement, cervi- presented in Tables 5 and 6. For dilation, comparison of cal examination students were exactly correct signifi- model 1 and model 2 demonstrated significantly lower cantly more often than the vaginal delivery students. interobserver variability in the cervical examination

Table 2. Final Assessment of Cervical Examination Table 3. Final Assessment of Cervical Examination Accuracy: Polyvinyl Chloride Models Accuracy: Silicone Models

Vaginal Delivery Cervical Vaginal Delivery Cervical Simulation Examination Simulation Examination Accuracy Analysis (n548) Simulation (n550) Accuracy Analysis (n527) Simulation (n530)

Dilation Dilation Exactly correct 5260.4 7360.2* Exactly correct 3860.2 5760.2* Within 1 cm 8260.2 9860.06* Within 1 cm 7760.2 8460.1 Effacement Effacement Exactly correct 5160.6 8360.1* Exactly correct 4560.3 6760.2* Within 1 cm 9660.1 100* Within 1 cm 7360.2 8860.1 Data are mean6standard deviation (in %) or %. Data are mean6standard deviation (in %). * P,.05 for vaginal delivery simulation compared with cervical * P,.05 for vaginal delivery simulation compared with cervical examination simulation. examination simulation.

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Copyright ª by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. Table 4. Comparison of Exact Accuracy: Polyvinyl a student who did and did not achieve competence Chloride Compared With Silicone Models during the clerkship are provided in Figure 3. The numbers of repetitions required to achieve competence Accuracy Analysis PVC Pipe (%) Silicone (%) for all of the cumulative summation analyses is pro- Cervical examination group vided in Table 8. Dilation 73619 53624* Effacement 83615 67621* DISCUSSION Vaginal delivery group Dilation 45626 39620 The results of the resident and attending surveys Effacement 67622 47629* indicate that both models would be useful in training and likely to improve trainee skill with labor cervical PVC, polyvinyl chloride. Data are mean6standard deviation (in %). examinations. Nearly all those surveyed felt the * P,.05 for polyvinyl chloride pipe compared with silicone models. silicone models were more realistic and would be more useful in medical student and resident training. students (P,.001). Significantly lower intraobserver Simulation training had a substantial effect on the variability was also demonstrated in the cervical exam- students’ cervical examination accuracy, because the ination students in the comparison of model 2 and cervical examination students performed better in model 3 (P5.003). Of the three models, the model with their assessments of dilation and effacement than the the best fit was the model that allowed both interob- vaginal delivery students in nearly all comparisons server and intraobserver variability to be heterogeneous with accuracies ranging between 4 and 32 percentage (model 3). Results were similar for effacement. points higher. Cervical examination students also The results of the comparison between experi- demonstrated 4.5-fold less intraobserver variability enced and inexperienced health care providers’ esti- for dilation and eightfold less for effacement. In addi- mations are provided in Table 7. Compared with the tion, their interobserver variability was threefold less medical students, the residents had significantly high- for dilation and 2.5-fold less for effacement. Thus, not er accuracy in their assessments of dilation. No differ- only did the training improve a trainee’s accuracy, but ences were seen in the accuracy of their assessment of it also improved the precision of their assessments. effacement. In addition to the effectiveness of the training and In the exactly correct cumulative summation the novelty of the investigation, our study has several analyses, 65% and 88% of the cervical examination other strengths. The first is the study’s size, because it students achieved competence in dilation and efface- included 98 students, which is approximately equal to ment, respectively. All cervical examination students the largest prior study of cervical examination accuracy achieved competence in assessment of dilation and using models.2 This prior study involved approxi- effacement in the within 1-cm analyses. Representative mately 1,500 examinations, whereas the present study graphs depicting the cumulative summation score in involved a total of approximately 4,000 examinations

Fig. 3. Representative cumulative summation analyses graphs. A. An example of a student who achieved competence during the clerkship. From the beginning of the clerkship the student was correct more often than he or she was incorrect. Thus, the line steadily decreased and competence was achieved when it crossed two threshold lines from above (arrow). B. An example of a student who did not achieve competence during the clerkship. From the beginning of the clerkship the student was incorrect more often than he or she was correct. Thus, the line steadily increased and competence was not achieved during the clerkship. Nitsche. Medical Student Cervical Examination Simulation. Obstet Gynecol 2015.

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Within-Participant Between-Participant Model Variance Variance ICC Comparison* P

1 0.075 0.465 0.860 2 0.053 CE: 0.24 0.82 Model 1 vs model 2 ,.01 VD: 0.73 0.93 3 CE: 0.028 CE: 0.27 0.90 Model 2 vs model 3 .003 VD: 0.13 VD: 0.70 0.85 ICC, interclass correlation coefficient; CE, cervical examination group; VD, vaginal delivery group. * Model 1, interobserver and intraobserver variability homogeneous; Model 2, interobserver variability heterogeneous, intraobserver variability homogeneous; Model 3, interobserver and intraobserver variability heterogeneous. with students receiving cervical examination training skill to master, only 65% of students were able to performing between 40 and 100 examinations. achieve competence after an average of 76 repetitions. Although the range of repetitions is wide, the rather So if the training were extended to the point at which small standard deviation (17) indicates most students all students achieved competence, it would be expected performed a similar number of examinations. Our sam- that the average number of repetitions needed to ple also had an equal gender distribution between achieve competence would rise. This suggests that if groups minimizing the previously described gender dif- the goal is to get all trainees to competence, as it would ferences in Objectively Structured Clinical Examina- be for obstetrics and gynecology or midwifery pro- tion performance.10,11 Finally, although all of the grams—training regimens with more than 100 repeti- previous studies used volunteers, in the present study, tions would be necessary. none of the students participating in the obstetrics and In our study we also describe a method for gynecology clerkship opted out of the study, removing tracking competence using the cumulative summa- volunteer bias and making our study more generaliz- tion method, which is its greatest strength. Many of able to the average trainee. the critical training parameters such as the level of Another strength of our study was the use of accuracy needed for competence or the number of a separate, higher fidelity model for the final assessments repetitions needed to achieve it have now been of 57 students. Because training with the polyvinyl elucidated. The wide range of the repetitions needed chloride pipe models led to improved accuracy with to obtain competence suggests that a common train- the more realistic silicone models, we have demonstrated ing regimen in which all trainees receive the same that the simulation training specifically improved the amount of training is not warranted and more students’ skill with the labor cervical examination and importantly is an inefficient use of time. Including that the increased accuracy was not merely the result of a cumulative summation analysis in a simulation familiarity with the polyvinyl chloride models. training regimen will allow a personalized, and Although the average number of repetitions objective, approach to each learner’sindividual needed to obtain competence in the exactly correct needs, allowing each trainee to practice until compe- analysis may seem small—44 for dilation and 32 for tent rather than until a predetermined number of effacement—some students did not reach competence repetitions has been completed or amount of time during the clerkship. For dilation, the more difficult has passed.

Table 6. Variability of Cervical Effacement Assessment

Within-Participant Between-Participant Model Variance Variance ICC Comparison* P

1 0.040 0.23 0.85 2 0.028 CE: 0.13 0.83 Model 1 vs model 2 ,.001 VD: 0.33 0.92 3 CE: 0.009 CE: 0.13 0.94 Model 2 vs model 3 ,.001 VD: 0.073 VD: 0.31 0.81 ICC, interclass correlation coefficient; CE, cervical examination group; VD, vaginal delivery group. * Model 1, interobserver and intraobserver variability homogeneous; Model 2, interobserver variability heterogeneous, intraobserver variability homogeneous; Model 3, interobserver and intraobserver variability heterogeneous.

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Copyright ª by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. Table 7. Comparison of Accuracy: Experienced A final potential weakness is the crossover design Compared With Inexperienced Health using the students who received vaginal delivery training Care Providers as the simulation-naive controls. Although it is possible that exposure to the vaginal delivery training had Accuracy Resident Medical Student a beneficial effect on the students’ ability to perform Analysis (n521) (n548) a labor cervical examination, we demonstrated a signifi- Dilation 62616* 43625 cant effect despite this potential bias toward the null Effacement 68615 67622 hypothesis, which further strengthens our findings. Data are mean6standard deviation (in %). In conclusion, the present study provides the first * P,.05 resident compared with medical student. objective assessment of the effect of simulation training on trainee performance of the labor cervical examina- A limitation of our study and a potential confound- tion. The study not only demonstrates the effectiveness ing factor is that students in the cervical examination of this type of training, but it also has defined many of group performed more real-life cervical examinations. the crucial training parameters utilizing the cumulative However, the absolute difference between groups was summation technique. This important information can very small, less than one cervical examination. In now be used to construct an evidence-based simulation addition,wewerenotableassessthestudents’ accuracy regimen to personalize the training for each learner when performing real-life cervical examinations on while objectively assessing their competence to inde- laboring patients. Thus, we cannot definitively say that pendently perform this central obstetric skill. the cervical examination training used in our study will lead to improvement in clinical performance. Unfortu- REFERENCES nately, the optimal assessment in laboring women is not 1. Tuffnell DJ, Bryce F, Johnson N, Lilford RJ. Simulation of feasible as many women are reluctant to be examined cervical changes in labour: reproducibility of expert assessment. by junior trainees and there is a known association of Lancet 1989;2:1089–90. chorioamnionitis with multiple cervical examinations. 2. Phelps JY, Higby K, Smyth MH, Ward JA, Arredondo F, Considering these issues, a final assessment in a simu- Mayer AR. Accuracy and intraobserver variability of simulated cervical dilatation measurements. Am J Obstet Gynecol 1995; lated environment is the best, and only, realistic option 173:942–5. available, particularly if the testing environment is dif- 3. Huhn KA, Brost BC. 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Copyright ª by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.