title: Pitfalls in ultrasonic cervical length measurement for predicting preterm birth.
abstract: OBJECTIVE
  To describe the anatomic and technical difficulties encountered with transvaginal ultrasound imaging of the cervix in a consecutive series of women at risk for preterm delivery.
  
  
  METHODS
  Three groups of women had cervical ultrasound examinations: those with histories of preterm birth, those with incompetent cervices, and those admitted for preterm labor that did not progress. Standardized ultrasound examinations of the cervix involved measuring the length of the endocervical canal, funneling length, and internal os dilation with and without fundal pressure.
  
  
  RESULTS
  Sixty consecutive women had transvaginal ultrasound examinations for assessment of the cervix. Forty-six had histories of preterm birth, five had incompetent cervices, and nine had arrested preterm labor. Six types of problems arose, which can be divided into anatomic or technical considerations, with an overall frequency of 27% (95% confidence interval 16%, 40%). Anatomic pitfalls that hampered identification of the internal os included an undeveloped lower uterine segment (n = 5), a focal myometrial contraction (n = 1), rapid and spontaneous cervical change (n = 1), and an endocervical polyp (n = 1). Technical pitfalls included incorrect interpretation of internal os dilation because of vaginal probe orientation (n = 7) and artificial lengthening of the endocervical canal because of distortion of the cervix by the transducer (n = 1).
  
  
  CONCLUSIONS
  We caution those who perform cervical length examinations to be wary of falsely reassuring findings due to potential anatomic and technical pitfalls.
authors.affiliation: Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas 75235-9032, USA. lmcdon@mednet.swmed.edu
authors.forename: N P
authors.initials: NP
authors.lastname: Yost
authors.forename: S L
authors.initials: SL
authors.lastname: Bloom
authors.forename: D M
authors.initials: DM
authors.lastname: Twickler
authors.forename: K J
authors.initials: KJ
authors.lastname: Leveno
mesh_terms: D002584:Cervix Uteri / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D007752:Obstetric Labor, Premature / Q000175:diagnosis*; D011237:Predictive Value of Tests; D011247:Pregnancy; D016216:Ultrasonography, Prenatal