o_1977r8vv9vk1ts2ms0kd8pksa.pdf

342 A. Lysikiewicz
The splenic artery, a branch of the celiac axis, can be
identified with color Doppler and, within its straight
segment, a Doppler velocity measurement can be carried
out. If done at an insonation angle of close to 08,
a high accuracy of such a measurement can be expected
[30, 31].
According to this study, the deceleration angle of
Doppler waveform correlates well (r = 0.68) with fetal
hemoglobin deficit (mean expected for gestational
age minus actual hemoglobin). Also splenic artery
mean velocity is a good predictor of fetal anemia, with
sensitivity approaching 100%. Although the authors reported
success in obtaining satisfactory blood flow waveforms
in 95% of patients, the procedure is highly specialized,
which limits its application.
Fig. 22.2. Fetal descending aorta Doppler velocity in the
anemic fetus
Blood flow mean velocity measured in the fetal
descending aorta was inversely correlated with fetal
hematocrit [27, 28]. Rightmire et al. [27] compared
the fetal umbilical artery Pourcelot index with fetal
hematocrit and a numerical correlation allowed for
retrospective development of a formula predicting
fetal hematocrit. Prospective clinical confirmation of
the accuracy of this method has not been published.
A similar study by Copel et al. [29] led to development
of formulas that had limited accuracy for predicting
fetal hematocrit when based on fetal descending
aorta Doppler velocities alone.
Descending aorta Doppler velocities were again
studied by Nicolaides et al. [17] and the conclusion
of this group did not support use of fetal descending
aorta Doppler velocities for prediction of fetal hematocrit.
A correlation with fetal hematocrit was shown
only when descending aorta velocimetry data was
analyzed in relation to gestational age [30]. The
authors concluded that the correlation, although statistically
significant, has no sufficient predictive value
for clinical application.
Splenic Artery
Renal Arteries
Limited information exists on blood flow in renal arteries
in Rh disease. Mari et al. [32] indicates improvement
in the pulsatility index before fetal intravascular
blood transfusion in anemic fetuses and return
of absent end-diastolic flow after transfusion.
The authors attribute these findings to fetal increase
in renal flow to eliminate excess fluid after transfusion.
Diagnostic applications of renal artery velocity
measurements in fetal anemia have not been established.
Umbilical Arteries
No significant correlation has been found between
umbilical artery S/D ratio, pulsatility index, or resistance
index and fetal anemia [33, 34]. Perhaps steady
placental resistance and consistent umbilical vessel
diameter does not alter systolic/diastolic flow ratio
even with increased flow of both.
Doppler velocimetry of the fetal umbilical artery
reflects fetal placental resistance. There is no evidence
that placental vascular resistance is affected by maternal
alloimmunization; hence, no changes in umbilical
artery indices should be expected.
Internal Carotid Artery
A significant association between the degree of fetal
anemia and the increase in mean velocity in the fetal
common carotid artery has been reported by Bilardo
et al. [34]. In their series of 12 fetuses with primary
anemia (previously untransfused) measurements were
made immediately before cordocentesis. They suggested
that increased fetal cardiac output associated
with fetal anemia is an underlying mechanism and
not the redistribution in blood flow that occurs in
chronic hypoxia in growth-restricted fetuses.
Middle Cerebral Artery
Middle cerebral artery peak blood flow velocity can
be visualized on an axial view of the cranium (Fig.
22.3).
Significant and consistent increase of peak flow velocity
in the MCA was seen in anemic fetuses when
measured at the bifurcation from the circle of Willis
and at an angle of insonation of < 308 [35]. This finding
was reported in several other studies [16, 36, 37],
including a multicenter clinical trial [7], and was linearly
correlated with the degree of fetal anemia (Fig.
22.4) [16].