title: Volumetric (3D) imaging reduces inter- and intraobserver variation of fetal biometry measurements.
abstract: OBJECTIVE
  To compare the inter- and intraobserver variation of fetal biometric measurements utilizing two-dimensional (2D) and three-dimensional (3D) ultrasound imaging.
  
  
  METHODS
  This prospective study, utilizing three pairs of doctors trained in sonography, evaluated singleton pregnancies in the mid-trimester. Measurements of the biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL) were taken in duplicate by each doctor using 2D imaging and then again using 3D volume datasets. Each set of paired doctors evaluated 12 patients. Inter- and intraobserver variation were calculated as the SD of the difference between paired measurements performed by the doctor pairs and by the individual doctors, respectively. Bland-Altman plots were used to visually compare measurement bias and agreement by 2D and 3D methods.
  
  
  RESULTS
  Inter- and intraobserver variation for 2D and 3D ultrasound were small. The intraobserver variation of HC, AC and FL was significantly lower for 3D compared with 2D ultrasound. Interobserver variation was not significantly different when measured with 2D and 3D ultrasound, with the exception of FL, which was lower when measured with 3D ultrasound. The Bland-Altman plots showed that in 95% of the measurements, the percentage difference between 2D and 3D ultrasound techniques was within 5.3%, 4.6%, 9.6% and 9.6% for BPD, HC, AC and FL, respectively.
  
  
  CONCLUSIONS
  2D and 3D fetal biometric measurements are reproducible. The use of 3D ultrasound significantly reduces intraobserver variation for HC, AC and FL and reduces interobserver variation for FL.
authors.affiliation: Fetal Medicine Unit, Department of Obstetrics and Gynaecology, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong. danielchan@cuhk.edu.hk
authors.forename: L W
authors.initials: LW
authors.lastname: Chan
authors.forename: T Y
authors.initials: TY
authors.lastname: Fung
authors.forename: T Y
authors.initials: TY
authors.lastname: Leung
authors.forename: D S
authors.initials: DS
authors.lastname: Sahota
authors.forename: T K
authors.initials: TK
authors.lastname: Lau
mesh_terms: D000005:Abdomen / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000196:embryology; D000886:Anthropometry / Q000379:methods; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000196:embryology; D047109:Fetal Development / Q000502:physiology*; D005865:Gestational Age; D006257:Head / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000196:embryology; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D015588:Observer Variation; D011247:Pregnancy; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal / Q000379:methods*