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134 D. Maulik
Pulsed-Wave Doppler Interrogation
Pulsed Doppler sonography has become the most frequently
used mode for umbilical arterial interrogation.
With a pulsed-wave duplex Doppler system, an obstetric
scan is initially performed, and loops of the umbilical
cord are identified. Unlike the continuous-wave
mode, pulsed-wave Doppler insonation permits selection
of the location in the cord for interrogation. As
discussed below, the site of interrogation in the cord affects
the configuration of the Doppler waveform.
Usually a free-floating portion of the cord is insonated.
The cursor line representing the beam path is aligned
to intersect the selected portion of the cord, and the
Doppler sample volume is placed in that location.
The Doppler mode is then activated, and the umbilical
arterial Doppler waveforms are obtained (Fig. 10.2).
Doppler Display and Archiving
The Doppler waveforms are exhibited on the video
monitor of the continuous-wave or the duplex device.
Being generated in real time, the waveforms are
scrolled from right to left on the screen. The screen
is frozen when appropriate signals are displayed, and
the desired measurements are performed on these waveforms.
Usually, three to five waveforms are measured,
and the individual results are averaged and shown on
the screen. The display along with the results can be
printed, and the print, can be archived. The display
and results may also be saved on a video tape recorder
when a duplex system is used and on an audio tape recorder
when continuous-wave insonation is used.
Descriptor Indices
of the Umbilical Arterial
Doppler Waveform
The Doppler frequency shift information from the
umbilical artery is predominantly utilized to assess
downstream impedance in the fetoplacental vascular
bed. As discussed in Chap. 4, it is accomplished by
calculating indices that analyze the pulsatility of the
waveform in an angle-independent manner. Of the
numerous indices described in the literature, the systolic/diastolic
(S/D) ratio, resistance index (RI), and
pulsatility index (PI) are most commonly used in
clinical practice. The relative merits of the commonly
used indices are discussed in Chap. 4.
The comparative diagnostic efficacy of the above
Doppler indices and the diastolic/average (D/A) ratio
for predicting adverse perinatal outcome was investigated
by Maulik and associates [1] in a prospective
blinded study in a high-risk pregnancy population. A
continuous-wave Doppler device with a 4-MHz transducer
was used. The analytic technique consisted of
the receiver operating characteristic (ROC) method,
which evaluates a test's ability to discriminate the diseased
from the nondiseased population. The ROC
curves showed that the RI had the best discriminatory
ability when compared with other Doppler indices,
and the PI fared the worst (Fig. 10.3). The area
under the ROC curve of these indices showed that
these differences were statistically significant (Table
10.1). Despite its limitations, the S/D ratio remains
the most widely used Doppler index for evaluating
the fetal circulation, especially for umbilical ar-
Fig. 10.2. Pulsed Doppler interrogation
of umbilical arteries.
Left: Two-dimensional
sonogram depicting the flow
mapping of the umbilical vessels
and placement of the
Doppler sample volume at the
umbilical arterial location.
Right: Umbilical arterial Doppler
waveforms