MEASURING FETAL VOLUME DURING LATE FIRST TRIMESTER BY THREE-DIMENSIONAL ULTRASONOGRAPHY USING VIRTUAL ORGAN COMPUTER-AIDED ANALYSIS

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 degrees: (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 degrees and 9 degrees 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 degrees or 9 degrees 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 degrees, which is relatively fast and allows analysis of fetal volume with good reliability and agreement. (E-mail: wpmartins@gmail.com) (c) 2013 World Federation for Ultrasound in Medicine & Biology.