Cervix Measurement Criteria

Using transvaginal imaging, take repeated measurements of the cervix until you get three measurements that meet all nine criteria listed below and that differ by less than 10%. Of these excellent measures, record the SHORTEST BEST. When submitting images for the CLEAR image review, reviewers recommend that participants not submit cervical images from a patient with an existing cerclage. Although CLEAR will accept cervical images obtained in women with a cerclage in place, sonographers should be aware that it can be more difficult to demonstrate the required landmarks in these patients.

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Cervix Measurement Criteria
  1. Measurement is taken on a transvaginal image:
    1. Transvaginal measurements are the gold standard for ultrasound cervix measurements.
    2. Short cervix can be missed on transabdominal scans.
  2. The transvaginal image is filled primarily with the cervix and the field of view is optimized for measurement:
    1. The cervix occupies approximately 75% of the image.
    2. the bladder is visibly empty or nearly so.
  3. The anterior width of the cervix equals the posterior width:
    1. The anterior cervical thickness is equal to the posterior cervical thickness.
    2. The echogenicity is similar both anterior and posterior.
    3. There is limited concavity created by the transducer.
  4. The maternal bladder is empty:
    1. The maternal bladder has a variable effect on the cervical length.
    2. The maternal bladder should be visibly empty or nearly so.
  5. The internal os is seen:
    1. The internal os is a small triangular area at the superior portion of the endocervical canal.
    2. The internal os is adjacent to the uterine cavity.
  6. The external os is seen:
    1. The external os is a small triangular area at the inferior portion of the endocervical canal.
    2. The anterior and posterior portions of the cervix come together at the external os.
  7. The endocervical canal is visible throughout:
    1. The endocervical canal is a linear echogenicity created by the interface between the anterior and posterior walls of the cervix.
    2. The canal extends between the internal and external os.
  8. Caliper placement is correct:
    1. Calipers are placed where the anterior and posterior walls of the cervix touch at the internal and external os.
    2. Calipers do not extend to the outer-­most edge of the cervical tissue.
    3. Calipers extend along the endocervical canal.
    4. If the cervix is curved two or more linear measurements are performed and the values added together to obtain the cervical length. Do not trace the cervical length.
  9. Cervix Mobility is considered:
    1. Insert transvaginal probe to view the cervix --- withdraw probe until the image blurs to reduce compression from the transducer, then reapply just enough pressure to create best image.
    2. Enlarge image (2/3 of screen).
    3. Apply mild suprapubic or fundal pressure for approximately 15 seconds to watch for funneling. Reduce probe pressure while fundal or suprapubic pressure applied.
    4. Obtain three measurements, use shortest best.
    5. Total exam time about 3-5 minutes.

Please contact us if you have suggestions or questions at CLEARSupport@perinatalquality.org.