In addition to the timing of colposcopy, we examined the effect of age, combined oral contraception, parity, and smoking status on the probability of finding a type 1 transformation zone. This probability declined with the age, with an odds ratio of 0.59 associated with a 10-year increment in age (P<.001) and with smoking status (OR 0.55 for current smokers versus nonsmokers, P<.001). The use of combined oral contraception significantly increased the likelihood of finding a type 1 transformation zone (OR 2.7, P<.001). Parous women had a lower probability of having a type 1 transformation zone than nulliparous women (OR 0.47, P<.001), which further declined with increasing parity (P<.001).
In multivariable logistic regression analysis, age, current smoking, and parity were still associated with a lower probability of observing a type 1 transformation zone, whereas use of a combined oral contraception was associated with an increased probability (Table 4). Adjusted for these factors, the increased probability of type 1 transformation zone in week 4 of the cycle was no longer statistically significant.
Table 5 illustrates the combined effects of these factors by showing the probability for a 30-year-old woman having a type 1 transformation zone, calculated by logistic regression. The highest probability (86%) found was for a nonsmoking nulliparous women taking combined oral contraception (95% CI 0.82–0.89), whereas only 54% (95% CI 0.48–0.61) of parous smokers not using combined oral contraception are likely to achieve a type 1 transformation zone.
The main impetus for proposing the International Federation of Cervical Pathology and Colposcopy transformation zone classification system5–7 was to introduce a standard nomenclature whereby transformation zone description and treatment could be reliably compared. The literature describing treatment of cervical intraepithelial neoplasia did not previously have a standard transformation zone nomenclature and had reference to excision, cone biopsy, or conization, inter alia. These terms mean different things to different researchers. Furthermore, the excision of a small type 1 transformation zone is considerably less than that of a large type 3. The transformation zone classification system of the International Federation of Cervical Pathology and Colposcopy aspires to clarify and standardize nomenclature. It is hoped that the use of a standard transformation zone type classification might reduce the subjective nature that is inherent in colposcopic examination and that using the system may result in more valid comparison of therapeutic interventions.
We reviewed our data to determine what effect the time of cycle and other variables had upon the type of transformation zone reported in women attending our colposcopy clinic for the first time. A satisfactory colposcopic examination depends crucially on complete visualization of the transformation zone,3 in particular its upper limit, that is, the squamocolumnar junction, where most dysplastic epithelial lesions are located.8,9 In this work, we report a large series of colposcopic examinations detailing the factors that influence the determination of transformation zone type.
Colposcopic examination in the follicular phase was not associated with better chance of fully visualizing the upper transformation zone limit. Surprisingly, the only evident effect was that the last week of the cycle was associated with a higher chance to observe a fully ectocervical squamocolumnar junction (ie, type 1 transformation zone). Indeed, using multivariable logistic regression analysis, we determined that this finding was no longer statistically significant (Table 5). Our data reveals no advantage to timing a colposcopy examination and contradicts traditional teaching and belief that the squamocolumnar junction shifts outwards during the menstrual cycle. It is accepted that unopposed estrogen affects cervical morphology, and this may be clinically useful in women having various gynecological interventions, such as intrauterine coil insertion, colposcopy, or hysteroscopy. Unfortunately, the effects do not appear to move the squamocolumnar junction ectocervically at colposcopy. Scheduling appointments for a particular time of the cycle may, therefore, increase the risk of nonattendance and is inconvenient for patients and clinic staff. It appears to have no role in routine colposcopy practice.
An unexpected finding of our study is the association of smoking with involution or retraction of the squamocolumnar junction into the endocervical canal. Smoking is only already known as a risk factor for cervical intraepithelial neoplasia and squamous cell carcinoma.10 Our data reveals a statistically negative effect of smoking on the likelihood of finding a type 1 transformation zone. Smoking patients are, therefore, exposed to a potential risk of colposcopic complication because of the difficulties in evaluating and treating endocervical transformation zones.
Our results show a significant influence of parity on the transformation zone visibility. Accepted teaching is that previous pregnancy increases the rate of squamocolumnar junction visibility. Reporting the colposcopic examination of 174 pregnant women, Ostergaard reported that colposcopic examination revealed an 80% likelihood of being able to see the squamocolumnar junction in parous women who underwent colposcopy during pregnancy.11 He reasoned that the predominant effect of previous pregnancy is to stimulate the endocervical migration of this junction. Our data would support this view.
The effects of age12–15 and oral contraception15,16 on squamocolumnar junction visibility has also been described and are confirmed by our data. Using a 10-year interval, we found a significant negative association between age and squamocolumnar junction visibility. Independent of the menopause per se, age reduces the chance for a patient to achieve a type 1 transformation zone.
The low rate of unsatisfactory colposcopic examination due to type 3 transformation zone observed in our study was a surprise to us and is worthy of comment. Previous cervical treatment, such as cervical conization or large loop excision of the transformation zone, is accepted as a major risk factor for unsatisfactory colposcopy due to cervical stenosis and endocervical squamocolumnar junction.17 Because the inclusion criterion was that the patient should be a first attendee, only 8.4% of patients had a history of previous treatment elsewhere (Table 1). This characteristic of our study population could, therefore, explain this situation. Moreover, because our primary ambition was to relate the time of cycle to the transformation zone type, we did not include in our study menopausal women, who are known to have higher probability of unsatisfactory colposcopy.15,18
Our work might be limited by the inherent biases of all retrospective analyses. However, we believe the specific design of our study dramatically reduced those biases. We considered only computerized stored data from the first attendance at our colposcopy clinic without any follow-up data. Moreover, the retrospective analysis allowed a reduction in the risk of observation bias. Colposcopists, indeed, even if not blinded to the timing of colposcopy, because they were not told about our interest in the influence of timing, were probably not influenced in the way they reported the transformation zone type. Finally, the main limitation of our study is that, of the 1,647 patients who could have been included, 347 (21.1%) were excluded because the date of the last menstrual period was missing.
Our study confirms the role of age and combined oral contraception on the position and visibility of the upper limit of the transformation zone. It also highlights the influence of smoking and parity. A completely ectocervical and fully visible transformation zone (type 1) is, therefore, more likely to be observed in a young nulliparous, nonsmoking woman using an combined oral contraception. A specific timing for colposcopy does not improve the visibility of the transformation zone and should not, therefore, be recommended.
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© 2008 The American College of Obstetricians and Gynecologists
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