title: Measuring fetal volume during late first trimester by three-dimensional ultrasonography using virtual organ computer-aided analysis.
abstract: Our aim was to determine whether rotating the fetus over its largest axis and reducing the rotational step angle can improve reliability/agreement of fetal volume measurements obtained with three-dimensional ultrasonography (3-DUS). Two observers acquired three 3-DUS data sets for a fetus with a crown-rump length between 45 and 84 mm. These observers determined the fetal volume using virtual organ computer-aided analysis (VOCAL), by three different methods, with a rotational step angle of 30°: (1) minimal manipulation of the 3-DUS data set, fetus rotated over any axis; (2) manipulation of the 3-DUS data set until the fetus could be seen in a standardized manner, fetus rotated over its anteroposterior axis; (3) same 3-DUS data set manipulation, fetus rotated over its longitudinal axis. Intra- and inter-observer reliability/agreement was determined with intra-class correlation coefficients and limits of agreement. In addition, we tested the method that provided the best reliability/agreement results using 15° and 9° of rotational step angles. The time taken to manipulate 3-DUS and determine fetal volume was recorded. The best intra- and inter-observer reliability/agreement results were observed when the fetus was rotated over its longitudinal axis. Reducing rotational step angle to 15° or 9° did not further improve reliability/agreement. The observer took approximately 1 min to determine fetal volume using this method. Our findings indicate that fetal volume should be determined by rotating the fetus over its longitudinal axis, at a rotational step angle of 30°, which is relatively fast and allows analysis of fetal volume with good reliability and agreement.
authors.affiliation: Department of Obstetrics and Gynecology, Medical School of Ribeirao Preto, University of Sao Paulo (DGO-FMRP-USP), Ribeirao Preto, Brazil.
authors.forename: Daniela A
authors.initials: DA
authors.lastname: Barra
authors.forename: Jailson C
authors.initials: JC
authors.lastname: Lima
authors.forename: Francisco
authors.initials: F
authors.lastname: Mauad Filho
authors.forename: Edward
authors.initials: E
authors.lastname: Araujo Júnior
authors.forename: Wellington P
authors.initials: WP
authors.lastname: Martins
mesh_terms: D000465:Algorithms; D049628:Body Size; D005260:Female; D005333:Fetus / Q000033:anatomy & histology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal / Q000379:methods*; D014584:User-Computer Interface
keywords: Gestational age; Reproducibility of results; Three-dimensional imaging; Ultrasonography