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206 L. Detti et al.
Fig. 14.11. Slopes for normal fetuses (dotted line), mildly
anemic fetuses (thin line), and severely anemic fetuses
(thick line). (From [64])
measurements in conjunction with serial amniocentesis
for Delta OD 450 because of the learning curve associated
with performing MCA Doppler [66].
Alloimmunization is also discussed in Chap. 22.
MCA-PSV in Other Causes of Fetal Anemia
Delle Chiaie et al. [59] found an inverse correlation
between MCA-PSV measurements and hemoglobin
values in fetuses at risk for fetal anemia due to red
cell alloimmunization and fetal parvovirus infection.
In a longitudinal multicenter study on fetuses at risk
for anemia resulting from parvovirus infection, the
measurement of MCA-PSV predicted fetal anemia
with a sensitivity of 94.1%. All cases with moderate
and severe anemia were detected either by MCA-PSV
alone or in combination with real-time ultrasonography
[67].
MCA-PSV may also be a useful test in cases of severely
anemic fetuses due to fetomaternal hemorrhages
[43]. An increased peak blood flow velocity
has been reported in cases of acute severe fetomaternal
hemorrhage [68].
Recently, it has also been reported that MCA-PSV
may be helpful for the diagnosis of anemia in twin±
twin transfusion syndrome following laser coagulation
of the placental vessels [69].
The MCA-PSV appears to be the best test for the
noninvasive diagnosis of fetal anemia. It is important
to emphasize that training sonographers and sonologists
is the ªconditio sine qua nonº for the correct
sampling of MCA-PSV.
The following steps are necessary for the correct
assessment of the MCA.
1. The fetus needs to be in a period of rest (no
breathing or movements).
2. The circle of Willis is imaged with color Doppler.
3. The sonographer zooms the area of the MCA so
that it occupies more than 50% of the screen. The
MCA should be visualized for its entire length
(Fig. 14.13).
4. The sample volume (1 mm) is placed soon after
the origin of the MCA from the internal carotid
artery (1±2 mm).
5. The angle between the direction of blood flow and
the ultrasound beam is as close as possible to zero
degrees. The angle corrector should not be used.
6. The waveforms (between 15 and 30) should be
similar to each other. The highest PSV is measured
(Fig. 14.14).
7. Repeat the above steps at least three times.
The MCA distal to the transducer can be an alternative
to the MCA proximal to the transducer [70];
however, the latter is preferable because it has the
lowest intra- and interobserver variability [71].
Maternal Antibody Titer (Indirect Coombs) > Critical Value
Fetus‘ Father Genotype
Homozygous Negtive for antigen Heterozygous or not available
Not other test necessary
A) Amniocentesis for fetal blood typing by PCR
B) Free fetal DNA in maternal plasma
Fetus does not have the antigen
MCA-PSV sequential studies
Fetus has the antigen
Fig. 14.12. Management algorithm
in pregnancies at risk of
having an anemic fetus because
of red cell alloimmunization