Journal of Ultrasound in Medicine, Vol 3, Issue 7 289-297, Copyright © 1984 by American Institute of Ultrasound in Medicine
The inaccuracy of total uterine volume measurements: sources of error and a proposed solution
A. B. Kurtz, W. M. Shaw, R. J. Kurtz, M. D. Rifkin, M. E. Pasto, C. Cole-Beuglet, O. H. Baltarowich, R. J. Wapner, P. M. Foy, P. M. Morgan and al. et
Inaccuracies in total intrauterine volumes calculated using the prolate
ellipse equation have been reported. No previous study has examined all the
sources of error. In this study, a comprehensive approach was undertaken.
Measurements were obtained from scans of the pregnant uterus in the prone
position using an automated water-path scanner (Octoson) and in the supine
position using standard static B-mode scanners. Several conclusions could
be drawn: 1) From the Octoson prone scans, uterine volumes obtained using
the prolate ellipse formula were markedly different from the true uterine
volumes obtained by the summation of stepped areas. This showed that the
prolate ellipse formula was inaccurate. 2) From the static supine scans,
many observer inconsistencies were found in uterine volumes obtained from
the prolate ellipse formula. This made the prolate ellipse formula
unreliable. 3) Previously published graphs calculated from the prolate
ellipse equation, comparing fetal age with total intrauterine volume, were
found to vary accuracy, presumably as a result of 1 and 2. A more accurate
approach is proposed. Using the outer uterine wall as the boundary, the
stepped area-to-volume values of transverse scans taken at 3-cm intervals
were found to closely approximate true volumes, with an average error of
only 3.5 per cent. Since these measurements encompass the intrauterine
contents and the myometrium, it is suggested that the term "total uterine
volume" be used instead of "total intrauterine volume."
