o_1977r8vv9vk1ts2ms0kd8pksa.pdf

156 K. MarsÏ—l
Table 11.5. Follow-up study on neurologic and intellectual
performance of 149 children at 7 years of age a
Summary
Variable
Relative
risk
95%
Confidence
interval
Significant Aortic BFC 3.64 1.25±10.54
contribution Social group 2.82 1.12±7.07
to total IQ £85
Significant Aortic BFC 3.61 1.55±8.41
contribution
to minor neurologic
dysfunction
IQ, intelligence quotient; BFC, blood flow class.
a Results of logistic regression analysis [101, 102].
A combination of real-time scanning and pulsed Doppler
velocimetry is required for Doppler ultrasound
velocimetry of the fetal descending aorta. A combined
linear array real-time/pulsed Doppler method makes
it possible to estimate fetal aortic volume flow. However,
the volume flow method is open to error and is
therefore less suitable for application to the clinical
situation. The waveform of the maximum velocities
recorded from the fetal descending aorta reflects the
impedance to flow in the placenta and the lower fetal
body. The waveform is also influenced by other factors
(e.g., fetal heart function). The aortic waveform
can be characterized by various indices (e.g., the PI
and the RI). In a situation of increased peripheral
vascular resistance, the aortic diastolic velocities decrease
and eventually disappear. In extreme cases reversed
flow during diastole can be detected. The finding
of absent or reversed aortic flow is associated
with an adverse outcome of pregnancy. For practical
application, a semiquantitative method (blood flow
classes) has been designed to evaluate fetal aortic
velocity waveforms. The BFC method emphasizes
especially the appearance of the diastolic part of the
waveform. When recording fetal aortic Doppler signals,
caution must be taken to avoid periods of fetal
breathing movements, which can profoundly influence
the shape of the waveform. The values of waveform
indices in the fetal aorta are also dependent on
fetal heart rate and activity/behavioral states.
In uncomplicated pregnancies the velocity waveform
of the fetal descending aorta shows positive flow
throughout the cardiac cycle, the proportion of diastolic
flow being higher in the abdominal aorta than
in the thoracic aorta. The PI values are stable during
the last trimester of gestation, with a slight increase
at term. The aortic mean velocity and the relative
flow do not change significantly with gestational age
during late pregnancy. About 50%±60% of the flow in
the thoracic descending aorta supplies the placenta.
In fetuses with a cardiac arrhythmia, aortic Doppler
velocimetry can facilitate diagnosis of the arrhythmia,
and the estimation of aortic flow can provide
an early indication of imminent heart failure. In
anemic isoimmunized fetuses, the mean aortic velocity
is increased.
Clinical studies of pregnancies with IUGR showed
that examination of fetal aortic velocity waveforms
can be used for fetal surveillance. The develoment of
fetal hypoxia is associated with typical changes of the
waveform: increased PI and absence or reversal of
diastolic flow. These changes usually precede other
signals of fetal distress. The predictive capacity of fetal
aortic velocimetry is comparable to that of umbilical
artery velocimetry with regard to IUGR and the
development of fetal distress. As is the case for umbilical
artery velocimetry, Doppler examination of the
fetal descending aorta is suited for application as a
secondary diagnostic test in high-risk pregnancies.
Changes in the intrauterine aortic waveforms have
been shown to be significantly correlated to the perinatal
outcome and to the long-term postnatal neurologic
and psychological development. Analysis of the
fetal aortic flow velocity pattern can be applied, together
with examination of other vessel areas, for a
more detailed study of redistribution of flow in the
presence of fetal hypoxia. Clinical management protocols
based on such a concept should be tested in prospective
randomized trials.
References
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of human fetal circulation using ultrasound: a
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