title: Pitfalls of ultrasonographic yolk sac measurement.
abstract: OBJECTIVE
  Novel aneuploidy screening has been suggested for measuring the yolk sac during very early pregnancy. However, in a pilot study the measured diameters differed up to 29 % from the overall average. The aim of this study was to analyze the impact of image magnification on yolk sac measurement.
  
  
  METHODS
  From November 3, 2009 to July 28, 2010, 119 yolk sac measurements were performed. During each examination, each yolk sac was examined once with standard image magnification and once by live scan zoom.
  
  
  RESULTS
  The measurement values were 5 % smaller in the standard image. The mean relative ratio (RR), median RR, and standard deviation (SD) were 0.951, 0.950, and 0.103 mm, respectively (95 % CI 0.744 to 1.158 mm). Regarding absolute differences, the mean, median, and standard deviation were -0.222 mm, -0.220 mm, and 0.473 mm, respectively, (95 % CI -1.169 to + 0.725 mm). With standard zoom (magnified images), the SD was 1.142 mm (1.099 mm).
  
  
  CONCLUSIONS
  Five criteria should be regarded for optimal image settings: image magnification during live scan, optimal gain setting, enhanced gamma level, median section plane, and out-to-out caliper placement.
authors.affiliation: Frauenarztpraxis Bahnhofstraße, Wolfenbüttel. info@dr-schmidt.info
authors.forename: P
authors.initials: P
authors.lastname: Schmidt
authors.forename: C
authors.initials: C
authors.lastname: Hörmansdörfer
authors.forename: M
authors.initials: M
authors.lastname: Elsässer
authors.forename: A
authors.initials: A
authors.lastname: Scharf
authors.forename: P
authors.initials: P
authors.lastname: Hillemanns
authors.forename: C S
authors.initials: CS
authors.lastname: von Kaisenberg
mesh_terms: D000782:Aneuploidy; D002869:Chromosome Aberrations; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D010865:Pilot Projects; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011785:Quality Assurance, Health Care / Q000592:standards; D012016:Reference Values; D012307:Risk Factors; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal / Q000379:methods*; D015017:Yolk Sac / Q000000981:diagnostic imaging*