title: Longitudinal z Score Distribution in Sonographic Fetal Biometry: Influence of Examiner and Experience.
abstract: OBJECTIVE
  To analyze the influence of examiners and their experience on the quality of biometric measurements via the evolution of z scores in a longitudinal multicenter study.
  
  
  METHODS
  This retrospective study included 4607 sonographic fetal biometric examinations performed by 18 examiners at the beginning of their sonography training. To analyze the quality of biometric measurements, z scores comparing the individual measurements with the expected values from a standard population were computed. To investigate the effect of examiners and their experience, we applied a multivariable regression analysis via generalized additive mixed models.
  
  
  RESULTS
  Mean z scores for biparietal diameter, abdominal circumference, and femur length were statistically different from the expected value of 0 (P < .001); no significant differences were found for head circumference measurements. Regression analyses showed a significant effect of the number of examinations on the distribution of z scores for each type of measurement. This effect yielded z score values close to the expected value of 0 at 100 to 200 examinations for all biometric measurements, indicating good consistency with the distribution of values in the reference population. Near the end of the study period, an increasing tendency toward either overestimation (head circumference) or underestimation (biparietal diameter, abdominal circumference, and femur length) was observed.
  
  
  CONCLUSIONS
  A longitudinal analysis of the z score distribution for quality control of biometry is feasible. A prospective and automatized use of this technique could help identify potential systematic errors and therefore improve the detection rate for high-risk pregnancies.
authors.affiliation: Department of Obstetrics and Gynecology, University Hospital of Erlangen, Erlangen, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Faschingbauer
authors.affiliation: Department of Obstetrics and Gynecology, University Hospital of Erlangen, Erlangen, Germany.
authors.forename: Jutta
authors.initials: J
authors.lastname: Heimrich
authors.affiliation: Department of Obstetrics and Gynecology, University Hospital of Erlangen, Erlangen, Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Raabe
authors.affiliation: Department of Obstetrics and Gynecology, University Hospital of Erlangen, Erlangen, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Kehl
authors.affiliation: Department of Obstetrics and Gynecology, University Hospital of Erlangen, Erlangen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Schneider
authors.affiliation: Department of Medical Informatics, Biometry, and Epidemiology, Rheinische Friedrich-Wilhelms-University of Bonn, Bonn, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Schmid
authors.affiliation: Department of Obstetrics and Gynecology, University Hospital of Erlangen, Erlangen, Germany.
authors.forename: Matthias W
authors.initials: MW
authors.lastname: Beckmann
authors.affiliation: Department of Obstetrics and Perinatal Medicine, Perinatalzentrum Hannover, Diakonischen Dienste Hannover Frauenkliniken, Hannover, Germany.
authors.forename: Ralf L
authors.initials: RL
authors.lastname: Schild
authors.affiliation: Department of Medical Informatics, Biometry, and Epidemiology, Rheinische Friedrich-Wilhelms-University of Bonn, Bonn, Germany.|Department of Medical Informatics, Biometry, and Epidemiology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Mayr
mesh_terms: D001699:Biometry / Q000379:methods*; D002983:Clinical Competence / Q000706:statistics & numerical data*; D003430:Cross-Sectional Studies; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000196:embryology; D047109:Fetal Development / Q000502:physiology*; D020567:Fetal Weight / Q000502:physiology*; D006801:Humans; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008297:Male; D011247:Pregnancy; D015203:Reproducibility of Results; D012189:Retrospective Studies; D016216:Ultrasonography, Prenatal / Q000706:statistics & numerical data*
keywords: biometry; examiner experience; fetal weight estimation; obstetric ultrasound; sonography; z scores