• Angtuaco TL, Gupta N, Andreotti RF, Lee SI, DeJesus Allison SO, Horrow MM, Javitt MC, Lev-Toaff AS, Scoutt LM, Zelop C, Expert Panel on Women's Imaging. ACR Appropriateness Criteria® assessment of gravid cervix. [online publication]. Reston (VA): American College of Radiology (ACR); 2008. 5 p. [33 references]

This is the current release of the guideline.

This guideline updates a previous version: Fleischer AC, Andreotti RF, Bohm-Velez M, Fishman EK, Horrow MM, Hrocak H, Thurmond A, Zelop C, Expert Panel on Women's Imaging. Premature cervical dilation. [online publication]. Reston (VA): American College of Radiology (ACR); 2005. 7 p. [27 references]

The appropriateness criteria are reviewed annually and updated by the panels as needed, depending on introduction of new and highly significant scientific evidence.

ACR Appropriateness Criteria®

Clinical Condition: Assessment of Gravid Cervix

Variant 1: Patient not at risk for preterm delivery: 16-24 weeks gestation; cervix <3 cm long or suggestion of funneling by transabdominal ultrasound examination.

Variant 2: Patient at risk for preterm delivery (history of prior preterm birth or multiple gestations): 16-24 weeks gestation: cervix <3 cm long by transabdominal or transvaginal ultrasound examination.

Summary of Literature Review

The term cervical incompetence was first introduced in 1948 by Palmer and Lacomme. This condition, which is characterized by painless midtrimester cervical dilatation, has a reported incidence of 1% and may be responsible for as many as 20% of second trimester miscarriages.

As a result of recent investigations that recognize features shared by women with cervical incompetence and those with premature labor, the concept of cervical incompetence as an "all or none" phenomenon has been challenged. Cervical incompetence is believed to represent a continuum that relates to cervical length and pregnancy history.

Regardless of the precise definition for this condition, there is no debate that preterm birth (<37 weeks of gestation) continues as the leading cause of perinatal morbidity and mortality. Consequently, it remains a major obstetrical challenge. Various methods for diagnosing preterm cervical dilatation have been proposed.

Digital Examination

Initial assessment is usually clinical and is based on digital palpation of the cervix. This examination can detect changes in cervical texture such as softening (which occurs as a precursor to delivery), and it can appreciate distensibility of the external os. These findings occur relatively late in the process of cervical dilatation, however, and in some cases are found too late to be reversed. Further, some physicians question the accuracy of digital measurements, which consistently underestimate measurements made by transperineal or transvaginal ultrasound (US). Most likely, this inaccuracy is due to the anatomic configuration of the cervix because the portion of cervix that lies above the anterior fornix or above the bladder base is hidden from the examiner's fingers. The digital examination has other limitations: 1) it is a subjective assessment; 2) the internal cervical os, which reflects initial changes associated with premature cervical dilatation, is beyond the examiner's reach; and 3) there are potential side effects that include risk of infection and ruptured membranes.

Nonetheless, if a patient is clinically at risk for preterm delivery, or if the US examination detects a short cervical length, some obstetrician-gynecologists may perform a digital cervical examination. Once the patient is near term (>37 weeks), and early delivery is no longer an issue, this examination can be omitted, unless clinically indicated for other reasons. To optimize the results and patient management, it is important to correlate the findings of the ultrasound examination with the digital examination.

Sonographic Examination

Unlike digital examination, sonographic measurements of cervical length generates an image that may be reviewed and standardized, thus overcoming subjectivity.

Normal-appearing cervix: During pregnancy, the length of the cervix does not elongate appreciably. Most authorities consider 3.0 cm in length as the lower limit of normal.

Transabdominal evaluation: Although most obstetrical sonographic examinations are done transabdominally, it is the least reliable imaging method for evaluating the cervix. Using this approach, bladder overdistension as well as myometrial contractions can change the appearance of the lower uterine segment and cervix, creating a deceivingly normal appearance in women with cervical effacement, shortening, or frank dilatation. Furthermore, an underdistended bladder may preclude adequate cervical visualization for any one of a variety of reasons: acoustic shadowing from the pubic symphysis, refractive shadowing from the bladder-uterine interface, and loss of the acoustic window provided by the urinary bladder and/or amniotic fluid, or an inability to manually displace the fetal head or other presenting part superiorly away from the lower uterine segment. Even when visible on a transabdominal scan, the cervical image is usually suboptimal. Because the external os is often not clearly identified, a technically correct cervical length measurement may not be possible. Therefore, if a patient has a clinical history or sonographic findings suspicious for cervical pathology, consideration should be given to cervical scanning using either a transperineal or transvaginal approach.

Transperineal/transvaginal evaluation: These approaches are the most accurate for assessing the cervix, although bladder distension and myometrial contractions may still give a falsely normal cervical appearance. When the cervix is well visualized, transperineal US can predict preterm delivery as accurately as transvaginal US. Cervical length is determined as the distance between the internal and external os. The internal os is normally at the level where the cervical canal meets the amniotic sac. The external os is often more difficult to define precisely because of acoustic shadowing from rectal gas. This problem can be minimized by either scanning the patient in a lateral decubitus position, or by elevating the hips and buttocks on a thick pad or pillow.

In patients at risk for cervical shortening or incompetence, some investigators suggest performing a cervical "stress test" by either applying transfundal pressure while scanning transvaginally, or examining the patient while she is standing. Because some patients will initially have a completely normal-appearing cervix, these important maneuvers may identify additional women who may require treatment for preterm cervical dilatation. If the cervix is already dilated or short, the cervical stress test may not be necessary because it may compound the problem by inducing further dilatation and shortening.

Abnormal-appearing cervix: Although the clinical presentation varies, from an imager's point of view cervical changes are essentially identical in patients in term labor, preterm labor, or cervical incompetence. In each of these clinical situations, cervical dilatation begins proximally, at the level of the internal os, and progresses distally. As the internal os dilates, membranes and amniotic fluid invaginate into the proximal endocervical canal. The most accepted terminology for these changes is funneling, although wedging or beaking have also been used. The disruption of the internal os, as documented by funneling, is a significant risk factor for adverse perinatal outcome. Cervical funneling is best described as a categorical variable (present or absent). In fact in a large series of 1,958 patients, the mean gestational age at delivery was significantly lower in the group with funneling compared with the group without funneling.

Eventually the entire endocervical canal becomes filled with fluid, and if the membranes remain intact, they may be visible bulging into the vagina. Concurrent with dilatation, the cervix becomes effaced and shortened. Dilatation and effacement typically progress simultaneously, although, in a given patient, one or the other event may appear to predominate. Investigators have recommended quantifying these cervical changes using a variety of measuring techniques, but the simplest and most reproducible measurement in sensitivity and predictive value appears to be the residual closed length of cervix. This calculation, which takes into account both dilatation and effacement, can be obtained by measuring from the distal apex of endocervical funneling at the internal os to the external os. Analysis by one study of low-risk pregnancies studied with transvaginal US indicates that using a cutoff value for cervical length of 33.15 mm yields an 80% sensitivity for predicting preterm delivery. This cutoff value resulted in a 12.7% false positive rate. Another multicenter observational study done for cervical length on transvaginal US from 16 to 24 weeks gestation categorized short cervical lengths as less than 25 mm, 25-29 mm, and 30 mm or greater. In both, the less than 25 mm group and 25-29 mm group, the incidence of spontaneous midtrimester birth (<26 weeks) was higher than the incidence of later (26-34 weeks) preterm birth (<25 mm group: 37% versus 19%; 25-29 mm group: 16% versus 3%, respectively) as compared with women with a longer cervical length of 30 mm or greater, who had rates of 1% and 9% respectively (p<.0001). Similarly, women who had an initial cervical length 30 mm or less and those who shortened their cervix to 30 mm or less before 22 weeks were also more likely to experience a midtrimester than later preterm birth. On the other hand, women whose cervix has shortened to 30 mm or less after 24 weeks or maintained a length greater than 30 mm had lower rates of midtrimester birth (p<.0001).

If a woman is clinically at risk for preterm delivery (such as prior preterm birth and multifetal gestation), or if a short cervix is detected by sonography, the precise length of the cervix should be measured and reported (this measurement is based on transperineal or transvaginal scans). Endocervical canal dilation of 2 to 4 mm during second-trimester endovaginal sonography has been associated with an increased risk of recurrent preterm delivery independent of cervical length. Studies have shown that serial transvaginal surveillance of cervical length in patients followed by cervical cerclage only when cervical changes are encountered appears to reduce the cerclage rate without compromising pregnancy outcome. In addition, in cases with visible dilatation, the sonologist should report the maximal endocervical diameter. The percent of "effacement" based on sonographic images is not reliable, because it is not possible to determine the location of the internal os once dilatation becomes apparent.

False negative diagnoses can occur during transperineal or transvaginal scanning if a cervical stress test is omitted. Some of the most challenging patients to evaluate are those in whom the appearance of the cervix changes during the sonographic examination. These transient but important observations underscore the need to observe the appearance of the cervix several times during a single obstetrical sonographic study, and suggest that a single image of the cervix may be insufficient for thorough cervical evaluation. A study of dynamic cervical change on 10-minute real-time US showed that minimum cervical length was a better predictor of preterm delivery than was initial cervical length. Another study demonstrated that on transvaginal US assessment of cervical length performed at 18, 24, 28 and 32 weeks gestation, shortening of cervical length ≥2.5 mm per week between 18 and 28 weeks' gestation also predicted preterm delivery. This is particularly the case in women at risk for preterm delivery, or those in whom a short cervix is detected by sonography. When a woman has transitory cervical changes, the minimal length of residual cervix should be reported, and the patient should be considered at risk. Clinical follow-up of these women reveals that 61% to 74% have preterm labor or deliver prematurely.

Summary

Transperineal and transvaginal sonography provides unique information about the cervix that is otherwise not readily available. These examinations are easy to perform, have been shown to predict the risk for preterm delivery and, in the appropriate clinical setting, should become an integral part of the obstetrical sonographic study.

None provided

The recommendations are based on analysis of the current literature and expert panel consensus.

• Angtuaco TL, Gupta N, Andreotti RF, Lee SI, DeJesus Allison SO, Horrow MM, Javitt MC, Lev-Toaff AS, Scoutt LM, Zelop C, Expert Panel on Women's Imaging. ACR Appropriateness Criteria® assessment of gravid cervix. [online publication]. Reston (VA): American College of Radiology (ACR); 2008. 5 p. [33 references]

Not applicable: The guideline was not adapted from another source.

1999 (revised 2008)

American College of Radiology - Medical Specialty Society

The American College of Radiology (ACR) provided the funding and the resources for these ACR Appropriateness Criteria®.

Committee on Appropriateness Criteria, Expert Panel on Women's Imaging

Panel Members: Teresita L. Angtuaco, MD; Nidhi Gupta, MD; Rochelle F. Andreotti, MD; Susanna I. Lee MD, PhD; Sandra O. DeJesus Allison, MD; Mindy M. Horrow, MD; Marcia C. Javitt, MD; Anna S. Lev-Toaff, MD; Leslie M. Scoutt, MD; Carolyn Zelop, MD

Not stated

This is the current release of the guideline.

This guideline updates a previous version: Fleischer AC, Andreotti RF, Bohm-Velez M, Fishman EK, Horrow MM, Hrocak H, Thurmond A, Zelop C, Expert Panel on Women's Imaging. Premature cervical dilation. [online publication]. Reston (VA): American College of Radiology (ACR); 2005. 7 p. [27 references]

The appropriateness criteria are reviewed annually and updated by the panels as needed, depending on introduction of new and highly significant scientific evidence.

None available

This summary was completed by ECRI on December 28, 2000. The information was verified by the guideline developer on January 25, 2001. This summary was updated by ECRI Institute on June 15, 2009.