title: Assessment of a cervicometer compared to transvaginal ultrasound in identifying women with a short cervical length: a multicenter study.
abstract: BACKGROUND
  Preterm birth remains a major cause of neonatal morbidity and mortality worldwide. Short cervical length (CL) as measured by transvaginal ultrasound (TVU) in the second trimester represents the single most predictive risk factor for spontaneous preterm birth. Previous studies have addressed, in part, the limitations of TVU availability by utilizing a cervicometer to screen patients for short cervix, identifying those patients who may not benefit from TVU CL screening. In view of the prior studies indicating that a cervicometer measurement may have a high negative predictive value (NPV) for a sonographically short cervix, we sought to identify the ideal cervicometer threshold value in a prospective, multicenter study.
  
  
  OBJECTIVE
  The primary objective was to determine the cervicometer CL measurement threshold that provides a high NPV for the identification of patients who are highly unlikely to have a TVU CL measurement ≤20 and ≤25 mm and, therefore, may forego TVU.
  
  
  METHODS
  This prospective study, executed in 5 US centers, included 401 women ≥18 years of age who provided written informed consent to undergo CL measurement in the mid trimester. All women underwent both cervicometer- and TVU-measured CLs by individuals blinded to results of the other measurement. Both measurements were performed at 17-23 weeks' gestation (visit 1) and repeated at 24-29 weeks' gestation (visit 2). All TVU measurement images were reviewed by a central reader. Test characteristics and receiver operating characteristic curves were created to determine and confirm the optimal cervicometer CL threshold, maximizing the NPV.
  
  
  RESULTS
  In all, 358 subjects were evaluable at visit 1 and 267 at visit 2. At visit 1, the average TVU CL was 38.7 ± 7.6 mm and the average cervicometer CL was 30.3 ± 8.8 mm. Similar measurements were seen at visit 2. Receiver operating characteristic curves were utilized to graphically identify a cervicometer CL threshold of 30 mm that maximized sensitivity while minimizing the false-positive rate. The 30-mm cervicometer CL threshold provided a 98-100% NPV and 0.0 negative likelihood ratio for identification of women who have a low likelihood to have a sonographic short cervix (ie, transvaginal CL ≤20 mm or ≤25 mm). The 17-23 weeks' gestation 30-mm cervicometer CL threshold has 100% sensitivity, 45-46% specificity, and 1.8 and 0.0 positive and negative likelihood ratios to predict sonographic CL ≤20 and ≤25 mm.
  
  
  CONCLUSIONS
  Cervicometer CL screening successfully identifies women at low risk for short transvaginal CL. Use of a 30-mm threshold by cervicometer CL measurement confers a 98-100% NPV, with high sensitivity and moderate specificity to predict a TVU short CL. Cervicometer measurement of CL may permit almost 50% of women to avoid TVU.
authors.affiliation: Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, PA. Electronic address: jason.baxter@jefferson.edu.
authors.forename: Jason K
authors.initials: JK
authors.lastname: Baxter
authors.affiliation: Department of Obstetrics and Gynecology, Section on Maternal Fetal Medicine, University of Tennessee College of Medicine, Chattanooga, TN.
authors.forename: C David
authors.initials: CD
authors.lastname: Adair
authors.affiliation: Department of Obstetrics, Gynecology, and Reproductive Sciences, Yale Medical School, Yale University, New Haven, CT.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Paidas
authors.affiliation: Christiana Care Health Services, Newark, DE.
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Hoffman
authors.affiliation: Blue Phoenix Biopharmaceutical Consulting, Dexter, MI.
authors.forename: Frances J
authors.initials: FJ
authors.lastname: Kivel
authors.affiliation: InClin Inc, San Mateo, CA.
authors.forename: Deb
authors.initials: D
authors.lastname: Cebrik
authors.affiliation: Cervilenz Inc, Chagrin Falls, OH.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Ross
mesh_terms: D000293:Adolescent; D000328:Adult; D054791:Cervical Length Measurement / Q000295:instrumentation* / Q000379:methods*; D002584:Cervix Uteri / Q000000981:diagnostic imaging*; D005260:Female; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D047928:Premature Birth / Q000517:prevention & control*; D011446:Prospective Studies; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D014463:Ultrasonography / Q000379:methods*; D055815:Young Adult
keywords: Cervilenz; biomarkers; prematurity; preterm birth; prevention; screening; short cervix