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ORIGINAL RESEARCH |
From the Department of Obstetrics and Gynecology, University Medical Center, Utrecht, The Netherlands; and the Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, New York University School of Medicine, New York, New York.
Address reprint requests to: Karolien Dijkstra, MD University Medical Center Room KE 04.123.1 Lundlaan 6, 3584 EA Utrecht The Netherlands E-mail: k.dijkstra{at}azu.nl
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Abstract |
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Methods: Eighty women whose primary physician determined that a prophylactic (n = 50) or urgent cerclage (n = 30) was indicated had transvaginal ultrasonographic evaluation before and after cerclage. Thereafter, most women had three additional transvaginal ultrasound examinations until 32 weeks’ gestation. At each examination, the mean of three measurements was calculated. Statistical analyses were done by t test, analysis of variance, and logistic regression, with significance set at P < .05.
Results: The mean ± standard deviation precerclage cervical length was 27.2 ± 10.3 mm and after cerclage was 34.1 ± 9.9 mm (n = 80, P < .001, paired t test). No significant association was found (r = -0.26) between the difference in cervical length (postcerclage - precerclage lengths) and pregnancy outcome. Patients with a prophylactic cerclage had a mean cervical length that was consistently longer in patients delivering at term compared with those who delivered preterm at 20 to 32 weeks’ gestation. In the urgent cerclage group a significant difference in cervical length between those who delivered at term compared with preterm was evident only at 28 to 32 weeks.
Conclusion: The increase in cervical length after cerclage is not predictive of term delivery. Serial cervical length measurements in the late second or early third trimester predict preterm birth but could provide earlier warning in patients with a prophylactic cerclage than in patients with urgent cerclage.
The measurement of cervical length by transvaginal ultrasonography has been used to assess the risk of preterm delivery in women with poor obstetric histories, potential preterm labor, cervical incompetence, and multiple pregnancies. There appears to be an inverse relationship between cervical length and risk of preterm delivery.1–3 Women who have a cervical cerclage for suspected cervical incompetence remain at increased risk for preterm labor and delivery. Historically, these women were followed up after cerclage using digital or speculum examinations, although some clinicians avoid vaginal examination.4
At present, the result of a cerclage procedure on cervical length can be viewed by transvaginal ultrasonography. Studies of postelective cerclage have shown some correlation with eventual pregnancy outcome.4,5 Andersen et al4 reported that a short upper cervical segment before 30 weeks’ gestation was associated with a significantly higher risk of preterm delivery before 36 weeks’ gestation. Rana et al5 also reported the importance of ultrasonographic follow up after cerclage. When early signs of cerclage failure or funneling were detected, immediate intervention with hospitalization and tocolysis was undertaken, which improved the final outcome of the pregnancy.
Recent studies showed that prophylactic, urgent, and emergency cerclage procedures resulted in measurable cervical lengthening.6–8 It is not known whether this relative restoration of cervical anatomy after prophylactic or urgent cerclage predicts pregnancy outcome. Our purpose was to determine whether the degree of cervical lengthening after cerclage predicts term delivery. The second aim of the study was to evaluate the usefulness of serial measurements of cervical length after cerclage, until 32 weeks’ gestation, to predict pregnancy outcome.
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Materials and Methods |
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Prophylactic cerclage (n = 50) was placed at 14.3 ± 2.8 weeks. The indication was a history of cervical incompetence (based on one or more of the following conditions: history of second-trimester pregnancy loss, history of diethylstilbestrol (DES) exposure in utero, cervical conization, and uterine anomaly) or a history of preterm birth with early cervical dilation without uterine contractions.
An urgent cerclage (n = 30) was placed at 19.7 ± 3.1 weeks in women with a cervical length shorter than 25 mm confirmed by transvaginal ultrasound before 24 weeks’ gestation.
Cervical length, defined as the length of the closed endocervical canal, was measured by transvaginal sonography using a 7.0-MHz probe (Acuson EV7, Acuson Corp., Mountain View, CA). In cases of cervical funneling, the apex of the funnel was considered the beginning of the closed endocervical canal, and the external os was considered the distal end of the endocervical canal.
In each case, after the woman emptied her bladder, the probe was inserted into the vagina until it met resistance. The probe was then withdrawn slightly to reduce compression, and three measurements were taken. The mean of the three measurements was used for analysis. None of the patients had contractions, bleeding, or discharge. None received prophylactic tocolysis, but some received prophylactic antibiotics at the discretion of the operator.
In 65 patients, a modified Shirodkar procedure as described by Frieden et al9,10 was done. In 15 patients a McDonald cerclage11 was placed, where the choice of suture material was left to the operator.
Seventy subjects were needed to achieve 80% power to detect a 30% difference in the rate of preterm delivery, with 
= .05. Cervical length measurements before and after cerclage between 20 and 32 weeks were compared using paired t test, analysis of variance, and logistic regression using JMP statistical software (SAS Institute, Cary, NC).
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Results |
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. No significant difference in baseline characteristics and in precerclage and postcerclage measurements was noted between patients who had Shirodkar compared with McDonald sutures. Mean gestational age at delivery was 36 weeks 4 days (95% confidence interval [CI], 35.4, 37.4 wk), and mean birth weight was 2760 g (95% CI 2567, 2952 g). In total, 32 women (40%) had a preterm birth (less than 37 completed weeks’ gestation) distributed in the same proportion in women with a prophylactic and urgent cerclage. The reasons for preterm birth were spontaneous preterm labor (ten women, 30%), preterm premature rupture of membranes (seven, 24%), induction for suspicion of intra-amniotic infection (three, 10%), indicated preterm birth (four, 12%), planned cesarean after determination of fetal lung maturity (four, 12%), and second-trimester loss (four, 12%).
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shows a decrease in cervical length over time in women who delivered before 37 weeks’ gestation. The mean cervical length, measured between 28 and 32 weeks, was significantly different in women who delivered preterm compared with those who delivered at term (21.0 ± 5.7 compared with 30.3 ± 9.5 mm, respectively; P = .002). The mean standard deviation of all measurements shown in Figure 1 is ±8.9 mm. Table 2 shows the mean cervical length and standard deviation before and after prophylactic and urgent cerclage. The association between cervical length before and after cerclage with pregnancy outcome in the prophylactic cerclage group is shown in Table 3. Cervical length before and after urgent cerclage related to pregnancy outcome is shown in Table 4. In the prophylactic cerclage group, the mean cervical length was consistently longer in women who delivered at term compared with those who delivered preterm at 20–23, 24–27, and 28–32 weeks’ gestation (Table 3). However, in the urgent cerclage group a statistically significant difference in cervical length between those who delivered at term comparing to those who delivered preterm was evident only at 28–32 weeks (Table 4).
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Discussion |
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The effects of cerclage in women believed to have incompetent cervices have been difficult to prove because many studies were limited because subjects were used as their own controls.6,12 It is likely that the historical difficulty in diagnosis of incompetent cervix makes it difficult to identify patients who might benefit from cerclage. Retrospective studies of cervical cerclage showed that cerclage increased obstetric intervention, as judged by admission to hospital, use of oral beta-mimetic agents, induction of labor, and cesarean delivery.13 A cerclage has an important beneficial effect in a minority of pregnant women.13,14 One randomized controlled trial has shown modest benefit in one in 25 operations, with a large 95% CI (one in 12 to one in 300 procedures).12 That study, likely the largest to date, used clinical uncertainty about placing a cerclage as the major eligibility criterion, reflecting the lack of standardized diagnosis.
Others have reported increased cervical length after cerclage. Funai et al,6 Althuisius et al,7 and Guzman et al8 agreed that a perioperative change in cervical length was a result of cerclage application. All described a significant cervical lengthening varying from 27 to 36 mm in 31 patients after prophylactic cerclage,6 from 21 to 34 mm in 34 patients after urgent cerclage,7 and from 2 to 27 mm in 29 patients after emergency cerclage.8 The differences in the various studies are mostly based on operative technique, method of ultrasonographic surveillance, indication for cerclage, and gestational age at cerclage placement. In our study, a difference was noted between the mean gestational age at placement of a prophylactic and an urgent cerclage (14.3 ± 2.8 weeks compared with 19.7 ± 3.1 weeks).
Andersen et al4 commented that perioperative cervical length measurements can be affected by the exact placement of the suture and can be increased falsely by a cerclage placed near the external os. Because of those results, we chose to measure only the length of the endocervical canal.
We studied the effect of cervical lengthening after the 72-hour postoperative period to predict birth outcome, as did Guzman et al.8 They showed that all patients continued to have progressive shortening of the upper cervix on serial postoperative examinations, with this measurement being less than 10 mm before 28 weeks’ gestation in all patients. In our study, serial postoperative examination results were similar, albeit only through measurements of the endocervical canal. The patients with continued cervical shortening after cerclage had an increased risk of premature birth compared with patients in whom the cervical length remained relatively constant during pregnancy.
Although it is not known whether the cervix is shorter in women with a multiple compared with a singleton pregnancy, we realize that women with multiple gestations have an increased risk of premature birth in comparison with singleton pregnancies. The 12 patients with a twin pregnancy and four with triplet gestation did not have cerclage placement because of multiple gestation. The indication was based on a history of cervical incompetence or was predicated on cervical shortening starting with a relatively short preoperative cervical length. However, when those patients were excluded from analysis, the results were not significantly different.
In both prophylactic and urgent cerclage groups there was a steady decrease in patients who delivered at term and in those who delivered preterm. However, patients who delivered at term retained the postoperative increase in cervical length longer, and then showed a more modest decrease in length over time compared with patients who delivered preterm. Further, in the prophylactic cerclage group, there was a statistically significant difference across gestational age (20 to 32 weeks) in mean cervical length in patients who delivered at term compared with those who delivered preterm. However, in the urgent cerclage group no statistically significant difference was noted until 28 to 32 weeks. Although serial assessment of cervical length is a valuable tool in assessing the risk of premature delivery, it might not be as useful a marker in patients who have urgent cerclage until much later in gestation.
It is not known whether patients with significant shortening of the cervix have other risk factors that influence the length of the cervix. Dijkstra et al15 showed that black women, women with severe stress, and women who are skilled manual laborers had significant shortening of the cervix in the same period of gestation, between 24 and 32 weeks. Unfortunately, the sample of black patients with sufficient cervical length measurements was too small to draw any conclusions. Information about stress and profession was not known in the present cohort of patients.
The relative risk of premature delivery increases as cervical length becomes shorter, so it is reasonable to hypothesize that prophylactic cerclage might reduce risk by restoring cervical anatomy, and this could be a greater barrier to ascending infection. In the present study, it was clear that the response of the cervix to cerclage, as defined by change in the length of the endocervical canal, did not predict pregnancy outcome. After cerclage, serial cervical length measurements with transvaginal sonography might be indicated to predict preterm birth if a progressive shortening of cervical length is noted in the late second or early third trimester. This shortening could alert the clinician to consider increased surveillance for signs and symptoms of preterm labor, utilization of fetal fibronectin testing, and limitation of physical activity. Also, one might consider corticosteroids to hasten fetal lung maturation. Although an increase in cervical length after cerclage was not predictive of outcome, progressive cervical shortening after cerclage was predictive of preterm delivery. It is not known why progressive cervical shortening occurs earlier in patients who have prophylactic cerclage than in patients who have urgent cerclage.
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Footnotes |
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Received October 25, 1999. Received in revised form February 18, 2000. Accepted March 2, 2000.
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References |
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2. Iams JD, Paraskos J, Landon MB, Teteris JN, Johnson FF. Cervical sonography in preterm labor. Obstet Gynecol 1994;84:40–6.
3. Iams JD, Goldenberg RL, Meis PJ, Mercer BM, Moawad A, Da A, et al. The length of the cervix and the risk of spontaneous premature delivery. N Engl J Med 1996;334:567–72.
4. Andersen FH, Karimi A, Sakala EP, Kalugdan R. Prediction of cervical cerclage outcome by endovaginal ultrasonography. Am J Obstet Gynecol 1994;171:1102–6.[Medline]
5. Rana J, Davis SE, Harrigan JT. Improving the outcome of cervical cerclage by sonographic follow up. J Ultrasound Med 1990;9: 275–8.[Abstract]
6. Funai EF, Paidas MJ, Rebarber A, O’Neill L, Rosen T, Young BK. Change in cervical length after prophylactic cerclage. Obstet Gynecol 1999;94:117–9.
7. Althuisius SM, Dekker GA, van Geijn HP, Hummel P. The effect of therapeutic McDonald cerclage on cervical length as assessed by transvaginal ultrasonography. Am J Obstet Gynecol 1999;180:366–70.[Medline]
8. Guzman ER, Houlihan C, Vintzileos A, Ivan J, Benito C, Kappy K. The significance of transvaginal ultrasonographic evaluation of the cervix in women treated with emergency cerclage. Am J Obstet Gynecol 1996;175:471–6.[Medline]
9. Shirodkar VN. A new method of operative treatment for habitual abortions in the second trimester of pregnancy. Antiseptic 1955;52: 299–300.
10. Frieden FJ, Ordorica SA, Hoskins IA, Young BK. The Shirodkar operation: A reappraisal. Am J Obstet Gynecol 1990;163:830–3.[Medline]
11. McDonald IA. Suture of the cervix for inevitable miscarriage. J Obstet Gynaecol Br Emp 1957;64:346–50.[Medline]
12. Grant AM. Final report of the Medical Research Council/Royal College of Obstetricians and Gynaecologists multicentre randomised trial of cervical cerclage. Br J Obstet Gynaecol 1993;100:516–23.[Medline]
13. Lazar P, Gueguen S. Multicentred controlled trial of cervical cerclage in women at moderate risk of preterm delivery. Br J Obstet Gynaecol 1984;91:731–5.[Medline]
14. Rush RW. A randomized controlled trial of cervical cerclage in women at high risk of spontaneous preterm delivery. Br J Obstet Gynaecol 1984:91:724–30.[Medline]
15. Dijkstra K, Janssen HCJP, Kuczynski E, Lockwood CJ. Cervical length in uncomplicated pregnancy. A study of sociodemographic predictors of cervical changes across gestation. Am J Obstet Gynecol 1999;180;639–44.[Medline]
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