o_1977r8vv9vk1ts2ms0kd8pksa.pdf

154 K. MarsÏ—l
Diabetes Mellitus
Serial Doppler examinations were performed in a
group of 40 pregnant women with diabetes mellitus
[80]. A high-volume blood flow in the fetal descending
aorta was found during the early third trimester;
near term, blood flow approached normal values. The
PI in the umbilical artery and fetal aorta was within
the normal range, so long as there were no signs of
fetal growth retardation or hypoxia. Otherwise no
flow variations specific for diabetic pregnancies were
seen. Similar findings were also reported for pregnant
women with gestational diabetes [81].
Intrauterine Growth Restriction
Intrauterine growth restriction (IUGR) can have various
etiologies, restricted flow through the placental
vasculature being the most common cause of this relatively
frequent complication of pregnancy. As described
above, the increased vascular impedance in
the placenta is reflected in a changed blood velocity
waveform in the descending fetal aorta, with a reduction
of diastolic velocities and a corresponding increase
in PI [6, 19, 35]. These findings are similar to
those reported for the umbilical artery of growth-retarded
fetuses [82].
In a study that evaluated placental morphology in
relation to intrauterine flow in IUGR fetuses, only the
presence of placental infarction was significantly associated
with abnormal flow velocity findings in the
fetal descending aorta (high PI, BFC I±III, low mean
velocity) [83].
In the descending aorta of growth-retarded fetuses,
low values were obtained for the time-averaged mean
velocity and volume flow, though they did not differ
significantly from those of controls [19]. This similarity
was probably due to the already mentioned methodologic
difficulty of precisely estimating volume
flow. Using an improved technique combining an ultrasonic
phase-locked echo-tracking system for diameter
measurement synchronized with a pulsed Doppler
velocimeter [16], Gardiner et al. [84] found both
the relative pulse amplitude, mean blood velocity, and
volume flow to be significantly lower in the descending
aorta of growth-restricted fetuses than in the controls.
Also, the aortic pulse waves of growth-restricted
fetuses showed values significantly different from
those in controls, reflecting the chronic ventriculovascular
responses to increased placental impedance
[85].
In severely growth-restricted fetuses developing
signs of intrauterine distress, the aortic end-diastolic
velocity disappears or even becomes reversed (BFC II
and III; Fig. 11.7) [18]. An association has been
found to exist between the degree of fetal hypoxia,
hypercapnia, acidosis, and hyperlactemia, as diagnosed
in blood samples obtained by cordocentesis
from growth-restricted fetuses and changes in the
mean fetal aortic velocity [86] and the velocity waveform
[87]. The aortic velocity waveform changes have
been observed to precede the cardiotocographic
changes, the median time lag being 2±3 days [19, 88],
though the interval between the first blood velocity
changes and the first changes in cardiotocographic
tracings may be as much as several weeks [19, 89].
The finding of ARED flow in the fetal aorta is associated
with an adverse outcome of the pregnancy
[19, 90] and increased neonatal morbidity [91, 92].
Reverse flow during diastole identifies fetuses in danger
of intrauterine death. Perinatal mortality in cases
with reverse flow is reported to be high ± in some series
as high as 100% [93]. The combination of ARED
flow in the fetal descending aorta and pulsations in
the umbilical vein seems to indicate a fetus with severe
hypoxia and iminent heart failure [18].
Aortic Doppler Velocimetry
as a Diagnostic Test of IUGR
and Fetal Hypoxia
Several prospective studies on IUGR pregnancies have
been performed to evaluate the predictive capacity of
fetal aortic velocity waveforms with regard to birth
weight, occurrence of fetal distress, and perinatal outcome.
Tables 11.3 and 11.4 summarize results of some
of the studies in terms of sensitivity, specificity, and
positive and negative predictive values. For the RI ratios
between the common carotid artery and descending
thoracic aorta of small-for-gestational-age (SGA)
fetuses redistributing their flow, a sensitivity of 94%
was reported for prediction of cesarean section for
fetal distress [96]. It is obvious that in IUGR fetuses
fetal aortic velocimetry is a better predictor of fetal
health than fetal size, which is not surprising in view
of the multiplicity of determinants of fetal growth.
The accumulated evidence suggests that, as is also
the case for umbilical artery velocimetry, Doppler fetal
aortic examination is better suited for use as a
secondary diagnostic test in preselected high-risk
pregnancies than as a primary screening test in a
whole pregnant population [97]. In a prospective
study of growth-retarded fetuses, Gudmundsson and
MarsÏ—l [90] compared the predictive value of aortic
versus umbilical artery velocity waveforms: The PI in
the umbilical artery was found to be a slightly better
predictor of fetal outcome than the aortic PI, though
the BFC was similarly predictive in the two vessels.
Two longitudinal studies confirmed that the changes
in the umbilical artery PI preceded changes in the