title: Optimal crown-rump length for measuring the nuchal translucency.
abstract: OBJECTIVE
  To determine the optimal crown-rump length (CRL) for obtaining nuchal translucency (NT) measurements.
  
  
  METHODS
  Women undergoing NT measurements by NT-certified sonographers within a combined screening program over an 18-month period were included in the study if they had a living fetus with a CRL of 45-84 mm. NT measurement success and screen-positive rates, transvaginal sonography (TVUS) use, and reasons for failed NT measurements were compared in 3 groups by CRL corresponding to 11-0/7 to 11-6/7 weeks (45-54 mm), 12-0/7 to 12-6/7 weeks (55-66 mm), and 13-0/7 to 13-6/7 weeks (67-84 mm).
  
  
  RESULTS
  Eight hundred thirty-seven women aged 34.9 +/- 4.9 years underwent 1 to 3 NT measurements at a mean CRL of 59.8 +/- 25.0 mm. NT measurements were more successful at 11 and 12 weeks (81.8% and 84.4%) than at 13 weeks (66.9%) (p < 0.001). Screen-positive and TVUS rates, and reasons for failed NT measurements did not vary by CRL.
  
  
  CONCLUSIONS
  NT measurements are most successful at CRL 45-66 mm corresponding to sonographically determined gestational ages of 11-0/7 to 12-6/7 weeks.
authors.affiliation: Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Maine Medical Center, 887 Congress Street, Suite 200, Portland, ME 04102.
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Wax
authors.forename: Michael G
authors.initials: MG
authors.lastname: Pinette
authors.forename: Angelina
authors.initials: A
authors.lastname: Cartin
authors.forename: Jacquelyn
authors.initials: J
authors.lastname: Blackstone
mesh_terms: D000328:Adult; D002869:Chromosome Aberrations; D015331:Cohort Studies; D018568:Crown-Rump Length; D004314:Down Syndrome / Q000000981:diagnostic imaging; D005260:Female; D005865:Gestational Age; D006801:Humans; D007713:Klinefelter Syndrome / Q000000981:diagnostic imaging; D008403:Mass Screening; D048208:Nuchal Translucency Measurement / Q000379:methods*; D011247:Pregnancy; D012189:Retrospective Studies; D016216:Ultrasonography, Prenatal