Objective
Adherence to published criteria for transvaginal imaging and measurement of cervical length is uncertain. We sought to assess adherence by evaluating images submitted to certify research sonographers for participation in a clinical trial.
Study Design
We reviewed qualifying test results of sonographers seeking certification to image and measure cervical length in a clinical trial. Participating sonographers were required to access training materials and submit 15 images, 3 each from 5 pregnant women not enrolled in the trial. One of 2 sonologists reviewed all qualifying images. We recorded the proportion of images that did not meet standard criteria (excess compression, landmarks not seen, improper image size, or full maternal bladder) and the proportion in which the cervical length was measured incorrectly. Failure for a given patient was defined as >1 unacceptable image, or >2 acceptable images with incorrect caliper placement or erroneous choice of the “shortest best” cervical length. Certification required satisfactory images and cervical length measurement from ≥4 patients.
Results
A total of 327 sonographers submitted 4905 images. A total of 271 sonographers (83%) were certified on the first, 41 (13%) on the second, and 2 (0.6%) on the third submission. Thirteen never achieved certification. Of 314 who passed, 196 submitted 15 acceptable images that were appropriately measured for all 5 women. There were 1277 deficient images: 493 were acceptable but incorrectly measured images from sonographers who passed certification because mismeasurement occurred no more than twice. Of 784 deficient images submitted by sonographers who failed the certification, 471 were rejected because of improper measurement (caliper placement and/or failure to identify the shortest best image), and 313 because of failure to obtain a satisfactory image (excessive compression, required landmarks not visible, incorrect image size, brief examination, and/or full maternal bladder).
Conclusion
Although 83% of sonographers were certified on their first submission, >1 in 4 ultrasound images submitted did not meet published quality criteria. Increased attention to standardized education and credentials is warranted for persons who perform ultrasound examinations of the cervix in pregnancy.
The American College of Obstetricians and Gynecologists (ACOG) recently issued a revised practice bulletin on prediction and prevention of preterm birth after publication of clinical trials that reported reduced risk of preterm birth in women with short cervix treated with progesterone supplementation. The ACOG Practice Bulletin notes that although progesterone supplementation “…has the potential to reduce the preterm birth rate…, (and) is cost effective, safe, accepted by patients, and widely available,” it also cautions that universal application of cervical length screening raises concerns about “…quality assurance of the screening test ( transvaginal cervical ultrasound )…and the potential for patients to receive unnecessary or unproven interventions.” Thus an improperly performed transvaginal ultrasound measurement of cervical length could be the cause of unneeded treatment, or of a missed opportunity to prevent preterm birth. These concerns highlight the importance of proper training and credentialing of persons who obtain and measure cervical ultrasound images, especially for a procedure that may become a part of routine prenatal care. Although there are published criteria to image and measure the cervix with transvaginal sonography, adherence to these criteria has not been assessed in research or clinical practice settings. Our objective was to assess the quality of transvaginal ultrasound images and cervical length measurements obtained by sonographers seeking credentials to participate in a clinical research study.
Materials and Methods
The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units (MFMU) Network has performed several studies in which transvaginal ultrasound images were obtained to measure cervical length. Sonographers who have performed cervical ultrasound for published network studies were required to review training materials and submit images for review to become certified before participating in the study. The training materials demonstrate the technique for obtaining an accurate, reproducible image; criteria for a satisfactory image; and proper caliper placement to measure cervical length. The instructions are summarized in Table 1 and the criteria in Table 2 .
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Image quality
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Measurement
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