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Chapter 10
Umbilical Doppler Velocimetry:
Normative Data and Diagnostic Efficacy
Dev Maulik
The umbilical artery was the first fetal vessel to be
evaluated by Doppler velocimetry and has since become
the most widely investigated component of the
fetal circulation. The attention paid to this vessel may
be explained partly by its ready accessibility to Doppler
interrogation, even without guidance by duplex
imaging, and because it is a vital component of the
fetal circulation, acting as the lifeline between the fetus
and the placenta. Numerous studies have reported
the methodology of Doppler interrogation of the umbilical
artery and have elucidated the factors that
modulate the umbilical arterial Doppler indices under
normal conditions. This chapter describes the procedure
of Doppler sonography of the umbilical circulation
and reviews the normative data on the umbilical
arterial Doppler indices.
Doppler Interrogation
of the Umbilical Artery
Doppler interrogation of the umbilical arterial circulation
is a relatively simple procedure that does not require
a large block of time. Consistent with the general
approach for conducting fetal surveillance tests, the
mother should be counseled regarding the reason for
the test, the nature of the information generated by
the device, its reliability and safety, and other relevant
issues. Similar to the practice for fetal heart rate monitoring,
the mother lies in a semirecumbent position
with a slight lateral tilt, which minimizes the risk of developing
supine hypotension syndrome due to caval
compression. The examination should be conducted
only during fetal apnea and in the absence of fetal hiccup
or excessive movement. Umbilical arterial circulation
is amenable to interrogation by either a continuous-wave
Doppler device or a pulsed-wave Doppler duplex
system. The procedure of Doppler insonation varies
with the choice of Doppler mode.
Continuous-Wave Doppler Interrogation
Continuous-wave Doppler interrogation of the umbilical
artery is one of the simplest procedures available
for fetal surveillance. However, it is now seldom used
in clinical practice. The procedure is conducted using
a freestanding Doppler instrument with an integrated
fast Fourier transform-based spectrum analyzer. The
transducer is usually a pencil-shaped probe with an
operating frequency of 2±4 MHz. The transducer is
placed on the mother's abdomen overlying the fetus
with an acoustic coupling jelly intervening between
the transducer face and the maternal abdominal skin.
The method is similar to that used for listening to fetal
heart tones with the simpler Doppler devices. The
transducer is systematically manipulated to obtain
the characteristic Doppler frequency shift waveforms
from the umbilical artery, which is seen on the device
display. The process of identification is facilitated by
listening to the typical audible sound of the Doppler
shift. The process of Doppler pattern recognition is
relatively simple, can be readily mastered, and is not
prone to significant subjective variations. Complete
Doppler interrogation of the cord can be ensured by
obtaining the umbilical venous Doppler signals simultaneously
with the arterial signals (Fig. 10.1).
Fig. 10.1. Continuous-wave Doppler interrogation of umbilical
vessels. Doppler frequency shift recordings above the
baseline are derived from the umbilical arteries, and those
below the baseline are from the umbilical vein