Soft Tissue Assessment for Fetal Growth Disorders
Wesley Lee
Baylor College of Medicine, Texas Children’s Pavilion for Women,
Houston, TX USA
Email: wesley.lee@bcm.edu
In a preliminary study, Akiba and colleagues report novel observations
about fetal limb soft tissue changes in Japanese women with gestational
diabetes as compared to gravidas with normal glucose tolerance (BJOG
2020 xxxx). No significant differences in fractional arm volume (AVol)
were found between groups until after 32 weeks gestation although
corresponding differences did not occur with fractional thigh volume
(TVol).
Three-dimensional ultrasonography now makes it feasible to evaluate
fetal soft tissue development in ways that were not previously possible
when based on 2D size parameters alone. For example, this technology
allows creation of standardized imaging planes for reliable extraction
of 2D soft tissue measurements (e.g. mid-thigh circumference or
subcutaneous fat thickness). Fractional limb volume, based on 50% of
long bone diaphysis length, can also be obtained (Lee W, et al.Ultrasound Obstet Gynecol 2009;33:427-40). These 3D volume
parameters demonstrate a linear relationship to menstrual age during
early pregnancy, from 18 weeks until approximately 28-29 weeks
gestation. Limb soft tissue accretion exponentially increases
thereafter. Akiba et al. have identified differences in this growth
process between AVol and TVol measurements at a time of accelerated soft
tissue deposition among diabetic gravidas.
Obstetricians traditionally rely on estimated fetal weight (EFW) as a
proxy for birth weight and as a key marker of neonatal nutritional
status. One should recognize that there are many different ways that EFW
could be calculated. Unfortunately, the vast majority of fetal weight
prediction models rely on 2D size parameters such as biparietal
diameter, abdominal circumference, and femur diaphysis length. Too much
emphasis is currently placed on skeletal structures that may not
accurately reflect body composition changes in malnourished fetuses.
Inclusion of limb soft tissue parameters with 2D size parameters now
adds a key nutritional component to the weight estimation process. This
capability offers new ways for characterizing changes in fetal body
composition associated with fetal growth disorders and neonatal growth
outcomes (Lee W, et al. Ultrasound Obstet Gynecol 2013;
41:198–203, Simcox LE, et al. Am J Obstet Gynecol2017;217:453.e1–453.e12, Roelants JA, et al. Pediatr Obes2017;12:65-71).
Newer sonographic approaches for evaluating fetal body composition are
often hampered by practical barriers for successful implementation into
clinical practice. Efficient methods for the noninvasive evaluation of
soft tissue development are required for fetal growth assessment. Future
technological advances could focus on the application of machine
learning and/or artificial intelligence methods for more rapid
fractional limb volume results without the need for manual tracing of
soft tissue borders. As grayscale imaging improves over time, these
improvements may help us to separate fetal soft tissue components (e.g.
fat, muscle, and bone) for further insight into body composition changes
in diabetic pregnancies. Robust characterization of prenatal soft tissue
development and its relationship to childhood obesity and health during
adult life raises many possibilities to be explored. Additional studies
could examine the level of maternal glucose control and fetal body
composition in different study populations. This line of investigation
may eventually lead to a new paradigm shift for how we could evaluate
fetal growth disorders going forward.
Disclosure of Interest: There are no conflicts of interest. A
completed disclosure of interest form is available to view online as
supporting information.