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.
- Exam is transvaginal
- Maternal bladder is empty:
- A full bladder can lead to inaccurate measurement.
- Field of view is optimized.
- The cervix should occupy 2/3 - 3/4 of the image field so that landmarks are clear.
- Anterior = posterior width of cervix
- A difference is typically due to excess pressure on the anterior cervix, which can lead to inaccurate measurement.
- Internal os is well seen
- The internal os is the small triangular area at the superior endocervical canal.
- External os is well seen
- The external os is the small triangular area at the inferior endocervical canal.
- Endocervical canal is visible in its entirety
- The endocervical canal is the linear echogenicity (of varying width and intensity depending upon presence of mucus) between the anterior and posterior cervix.
- Calipers are correctly placed
- The calipers are placed at the internal and external ostia where the anterior and posterior walls of the cervix touch, and the line between them constitutes the cervical length measurement.
- If the cervix is curved, 2 lines may be needed to characterize its entire length, however, if this is the case it is unlikely that the cervix is short.
- There may be confusion about whether to place the caliper at the pointy end or the blunt end of the triangle at the internal os. This decision requires clinical judgment and observation because a large triangle may simply represent mucus at the internal os (as opposed to funneling).
- Shortest, best of 3 measurements is reported
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