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Change in Cervical Length After Prophylactic Cerclage

From 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: Edmund F. Funai, MD, New York University School of Medicine, NB-9E2, 550 First Avenue, New York, NY 10016, E-mail: eff1{at}is4.nyu.edu

	Abstract

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Objective: To determine changes in length of incompetent cervices after cerclage, using transvaginal ultrasound.

Methods: Patients were enrolled in a prospective, observational study under an Institutional Review Board–approved protocol. McDonald or Shirodkar sutures were placed according to physician preference. Pre- and postcer-clage cervical lengths were measured within 72 hours of the procedure. At each examination, the first measurement was discarded, and a mean of the subsequent three measurements was calculated.

Results: Twenty-one Shirodkar and ten McDonald operations were done. The mean (± standard deviation) precerclage cervical length was 2.7 ± 0.9 cm and the postcerclage cervical length was 3.6 ± 0.9 cm (P < .001, paired t test).

Conclusion: Prophylactic cerclage results in measurable increases in cervical length, which might contribute to the success of the procedure. Further study is needed to determine whether the degree of cervical lengthening after cerclage predicts term delivery.

Ultrasonographic evaluation of cervical length and anatomy has been described in pregnant women without complications and those with preterm labor,^1,2 and there is an inverse relationship between cervical length and risk of preterm delivery.³ Measurement of cervical length by transvaginal ultrasound has become useful and is used frequently to assess risk of preterm delivery.

Women who have cerclages for suspected incompetent cervices continue to pose a challenge to obstetricians. Historically, women were followed after cerclage using digital or speculum examinations, although some clinicians avoid vaginal examination.⁴ Transvaginal ultrasound has been used to follow women recently, but the effects of prophylactic cerclage on cervical length are unknown. Our purpose was to determine the effect of prophylactic cerclage on cervical length, measured by transvaginal ultrasound before and after the procedure.

	Materials and Methods

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A prospective, observational study was conducted. Women whose primary physicians determined that prophylactic cerclage was indicated were approached to enroll in an Institutional Review Board–approved protocol. Diagnosis of incompetent cervix was based on history of second-trimester pregnancy loss, preterm birth with early cervical dilation without uterine contractions, or interval ultrasound confirmation of cervical shortening. Cervical length, defined as the length of the closed endocervical canal, was measured by trans-vaginal sonography using a 7.0-MHz probe (Acuson EV7; Acuson Corp., Mountain View, CA). Precerclage measurements were taken within 48 hours of the procedure. In each case, after the woman emptied her bladder, the probe was inserted into the vagina until it met resistance. The probe then was withdrawn slightly to reduce compression, and three measurements were taken. The mean of the three measurements was used for analysis. Postcerclage measurements were taken the same way within 72 hours of placement. Figure 1 is a representative image.

View larger version (127K): [in this window] [in a new window]   Figure 1. Calipers mark the internal (left) and external (right) os. The distance between the calipers was considered the cervical length. The cerclage can be seen in cross section.

None of the women had contractions, bleeding, or discharge. None underwent prophylactic tocolysis, but some received prophylactic antibiotics at the discretion of the operator. Modifications of procedures by Shirodkar⁵ and McDonald⁶ were used. The modified Shirodkar procedure was performed by the method of Young et al.⁷ Two sponge forceps were applied, one to the anterior and one to the posterior lip of the cervix. A 1-cm transverse incision was made anteriorly at the cervicovesical junction and posteriorly at the peritoneal reflection of the cervix. The bladder and peritoneum were mobilized cephalad past the internal os by sharp and blunt dissection. A 5-mm Mersilene band (Ethicon Inc., Somerville, NJ), doubly armed, was placed submucosally from posterior to anterior. The vaginal mucosa was closed posteriorly and over the knot to bury the Mersilene band and achieve hemostasis. The McDonald procedure was performed as described by McDonald,⁶ except that the choice of material varied according to individual operator.

Assuming a mean cervical length of 3.0 cm and a standard deviation (SD) of 0.5 cm, 17 subjects were needed to achieve 80% power to detect a 0.5-cm change in cervical length with = .05. Pre- and postcerclage cervical lengths were expressed in centimeters and compared by a paired t test, using JMP statistical software (SAS Institute, Cary, NC).

	Results

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Thirty-one women were studied; 21 Shirodkar and ten McDonald procedures were performed. Baseline characteristics of study subjects included a median age of 34.0 years (range 26–43), median gravidity of 5.0 (range 1–10), median of 1.0 (range 0–5) second-trimester loss, and median estimated gestational age at time of procedure of 15.0 weeks (range 12–24). Parity in our population was extremely skewed but ranged from 0 to 3 with a mode of 0.

The mean (± SD) precerclage cervical length was 2.7 ± 0.9 cm and the mean postcerclage cervical length was 3.6 ± 0.9 cm, a statistically significant difference (P < .001, paired t test).

	Discussion

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Prophylactic cerclage resulted in statistically significant increases in cervical lengths, potentially contributing to the success of the procedure. Change in cervical length after cerclage deserves further study as a possible predictor of term delivery.

The effects of cerclage in women believed to have incompetent cervices have been difficult to prove because many studies are limited by subjects’ being used as their own controls. It is likely that difficulty diagnosing and selecting patients made it hard to show clear benefit. One randomized, controlled trial showed modest benefit in one in 25 operations, with a large 95% confidence interval (one in 12 to one in 300 sutures).⁸ That study, likely the largest to date, used clinical uncertainty about placing a cerclage as the major eligibility criterion, which reflects the lack of standard in diagnosis. In the majority of those patients (71%), the indication was a prior second-trimester loss or preterm delivery.

Transvaginal ultrasound might be useful when combined with obstetric history and vaginal examination because a cervical length of less than 3 cm increased the risk a priori of preterm delivery.² In a larger study, using preoperative and postoperative cervical length measurements, it might be possible to show benefit in a larger proportion of women because a failing cervix might be identified better during gestation. Expectant management and serial ultrasound examinations might be more prudent in women with relatively long cervices.

Our study was similar to the work of Guzman and colleagues,⁹ who noted similar results in women treated with emergency cerclage. Those authors noted that cerclage resulted in improved sonographic status of the cervix and that the degree of increase in length correlated with pregnancy outcome. Another group⁴ measured the upper cervical segment (distance from cerclage to internal os) and noted that shortening was associated with premature delivery.

Those authors⁴ commented that measurement can be affected by placement of the suture and length can be increased falsely when the suture is placed near the external os. Because of those results, we chose to measure the length of the endocervical canal only, a relatively quick and easy measurement that correlates with gestational age at delivery in women who have emergency cerclage.⁹ We had no difficulty locating the internal os ultrasonographically but have had difficulty when measuring cervical length in the first trimester.

Compared with the women studied by Guzman et al,⁹ our subjects had cervices that were approximately 1 cm longer on average preoperatively (1.5 versus 2.5 cm). This is most likely due to the fact that our subjects had cerclage before emergency status was reached. The mean preoperative cervical length in our subjects was below the tenth percentile at 24 weeks’ gestation.³ The postoperative mean cervical length in our group was equal to the 50^th percentile based on the same data. Measurements were taken at a mean estimated gestational age of 15.9 weeks, an age at which nomograms have not been established. The women studied by Guzman et al⁹ had a median age of 28 years. Our subjects were older, but it is not known whether that difference in age contributed to cervical status.

The relative risk of premature delivery increases as cervical length becomes shorter, so it is reasonable to hypothesize that a prophylactic cerclage might reduce risk by restoring cervical anatomy. A larger study might show that the response of the cervix to cerclage, as defined by change in the length of the endocervical canal and degree of funneling, predicts pregnancy outcome.

	Footnotes

 
PII S0029-7844(98)00568-7

Received August 12, 1998. Received in revised form November 20, 1998. Accepted December 10, 1998.

	References

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1. Zorzoli A, Soliani A, Perra M, Caravelli E, Galimberti A, Nicolini U. Cervical changes throughout pregnancy as assessed by transvaginal sonography. Obstet Gynecol 1994;84:960–4.[Abstract/Free Full Text]

2. Iams JD, Paraskos J, Landon MB, Teteris JN, Johnson FF. Cervical sonography in preterm labor. Obstet Gynecol 1994;84:40–6.[Abstract/Free Full Text]

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.[Abstract/Free Full Text]

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. Shirodkar VN. A new method of operative treatment for habitual abortions in the second trimester of pregnancy. Antiseptic 1955;52: 99.

6. McDonald IA. Suture of the cervix for the inevitable miscarriage. J Obstet Gynaecol Br Empire 1957;64:346–50.[Medline]

7. Young BK, Freiden FJ, Odorica SA, Hoskins IA. The Shirodkar operation: A reappraisal. Am J Obstet Gynecol 1990;163:830–3.[Medline]

8. 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;100:515–23.

9. 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]

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