Journal of Ultrasound in Medicine, Vol 20, Issue 12 1283-1292, Copyright © 2001 by American Institute of Ultrasound in Medicine
Birth weight prediction by three-dimensional ultrasonography: fractional limb volume
W. Lee, R. L. Deter, J. D. Ebersole, R. Huang, K. Blanckaert and R. Romero
Department of Obstetrics and Gynecology, William Beaumont Hospital, Royal Oak, MI 48073-6769, USA.
OBJECTIVE: To introduce fractional limb volume as a new ultrasonographic
parameter, validate reliability of fractional limb volume measurements,
develop new birth weight prediction models, and examine their practical
utility for estimating fetal weight during late pregnancy. METHODS: Healthy
late-third-trimester fetuses were prospectively scanned by two- and
three-dimensional ultrasonography within 4 days of delivery. Volume data
sets were subsequently used to extract several standard ultrasonographic
measurements. Fractional limb volumes of the upper arm and thigh were based
on 50% of diaphyseal bone length. Intraclass correlation was used to
analyze interobserver and intraobserver reliability of fractional limb
volume measurements. Several weight prediction models were developed by
linear regression analysis. New prediction models were prospectively
compared with the Hadlock formula in 30 healthy late-third-trimester
fetuses. RESULTS: One hundred fetuses were scanned at a mean +/- SD
menstrual age of 39.2 +/- 1.2 weeks. Intraclass correlation indicated a
significant degree of interobserver and intraobserver reliability for
fractional thigh volume. Fractional thigh volume (r = 0.86), fractional
upper arm volume (r = 0.83), abdominal circumference (r = 0.83), and
midthigh circumference (r = 0.82) were most highly correlated with birth
weight. The best prediction model (abdominal circumference and fractional
thigh volume) gave weight estimates that deviated from actual birth weight
by -0.025% +/- 7.8%. For late-third-trimester fetuses, the Hadlock model
yielded errors of 9.0% +/- 9.0%. Prospective testing confirmed superior
performance of the new prediction model, which gave accuracy of 2.3% +/-
6.6% (Hadlock method, 8.4% +/- 8.7%). It correctly predicted 20 of 30 birth
weights to within 5% of actual weight. By comparison, the Hadlock model
predicted only 6 of 30 birth weights to within 5% of actual weight.
CONCLUSIONS: A new birth weight prediction model, based on fractional thigh
volume and abdominal circumference, is reliable during the late third
trimester. It provides a means for including soft tissue evaluation for
birth weight prediction. This rapid technique avoids technical limitations
that currently hinder the practical implementation of three-dimensional
ultrasonography for estimating birth weight.
