o_1977r8vv9vk1ts2ms0kd8pksa.pdf

204 L. Detti et al.
study confirmed that MCA-PSV is an accurate method
of monitoring pregnancies complicated by red cell
antibodies. In this study two anemic fetuses were
missed in a group of 125 fetuses at risk of anemia.
The interval between the last assessment of MCA-PSV
and the delivery in those two fetuses was 3.5 and
2.5 weeks. This suggested that a closer assessment of
MCA-PSV is necessary. This study also demonstrated
that the number of false positives increased following
35 weeks' gestation. A recent prospective study compared
MCA-PSV with Delta OD 450 in the prediction
of moderately and severely anemic fetuses [53]. The
authors concluded that both procedures are useful in
the prediction of fetal anemia, but Doppler ultrasound
assessment remains a method that has the advantage
of being less expensive and noninvasive than
amniocentesis. The MCA-PSV represents a more suitable
tool in the diagnosis and management of pregnancy
complicated by alloimmunizations than Delta
OD 450 [24, 54, 55].
The MCA-PSV performed prior to the first transfusion
has been used to estimate the real value of fetal hemoglobin
[56]. The difference between the observed
and calculated hemoglobin was lower in fetuses that exhibited
moderate to severe anemia compared with
cases when the fetus was mildly anemic (Fig. 14.8);
therefore, MCA-PSV performs better in cases of clinically
significant anemia. The explanation is that initial
small decreases in fetal hemoglobin only slightly
change cardiac output and blood viscosity. When the
anemia becomes more severe, these compensatory
Fig. 14.8. Quadratic function expressing the correlation of
percentage difference between the predicted and the actual
hemoglobin value and the hemoglobin multiples of
the median. (From [56]) Y =0.2876 ± 0.922 ´0.9498 ´ 2
mechanisms operate more to maintain the oxygen
and metabolic equilibrium in the various organs.
Intrauterine transfusion decreases fetal anemia significantly
and normalizes the value of fetal MCA-PSV
(Figs. 14.9, 14.10) due to an increased blood viscosity
and an increased oxygen concentration in fetal blood
[57]. The MCA-PSV may also be used for timing the
second fetal transfusion and the cut-off point to detect
severe anemia is higher than that used for nevertransfused
fetuses [58]. This is probably the consequence
of the different blood viscosity of the adult
blood when compared with the fetal blood.
Several other studies have confirmed the utility of
MCA-PSV for diagnosing fetal anemia [59±62]. This
parameter may also diagnose fetal anemia in dichorionic
twin pregnancies complicated by red blood cell
alloimmunization [63].
The above studies have used only one value of
MCA-PSV, which indicates whether the fetus is anemic
or not at the time of the evaluation; however, it
does not predict whether the fetus will become anemic.
In a longitudinal study, it has been shown that
the MCA slope is an excellent tool for identifying
those fetuses that will become severely anemic and,
therefore, need to be followed up more closely during
the pregnancy (Fig. 14.11) [64]. The same author suggested
the following protocol for monitoring pregnancies
at risk for fetal anemia due to red cell alloimmunization
[65]:
1. MCA-PSV should be performed in fetuses at risk
of fetal anemia on a weekly basis for three consecutive
weeks.
2. Cordocentesis is indicated when the MCA-PSV value
is over 1.5 MoM.
3. If the MCA-PSV remains below 1.5 MoM a regression
line has to be obtained from the following
three values.
If the plotted regression line is to the right of the
dotted line shown in Fig. 14.11, the examination has
to be repeated every 2 or 4 weeks based on the initial
risk of the patient ± with a lower initial risk (e.g., a
Coombs titer between 1 : 16 and 1 :32) the examination
can be repeated every 4 weeks, but with a higher
initial risk it should be repeated every 2 weeks. If the
plotted regression line is between the dotted and the
thin line (Fig. 14.11), the examination has to be repeated
every 1±2 weeks based on the initial risk to
the patient. If the plotted regression line is to the left
of the thin line and the MCA-PSV value is below
1.50 MoM, the examination has to be repeated in
1 week. Figure 14.12 represents the algorithm we use
for the management of pregnancies at risk of fetal
anemia because of red cell alloimmunization.
Centers with minimal experience with the assessment
of MCA-PSV should initially perform these