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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5817_Библиотеки_им_академика_М_И_Перельмана-1.pdf
Doppler Ultrasound Findings Near Term
Aorta: Qualitative Analysis
The effective breakthrough for Doppler ultrasound
came through the interpretation of the waveform of
the Doppler sonogram, either by itself or combined
with quantitative measurements. Impedance and
pulse wave reflections became more important for the
interpretation of Doppler sonograms than comparisons of blood flow volumes. In spite of technological
advances, it is easier to obtain qualitative rather than
quantitative results, especially since they are more or
less independent of the insonation angle.
As a result blood flow even in small vessels could be
analyzed, and so the aorta gradually lost its importance, while interest in the cerebral aa., as well as other
peripheral vessels such as the renal aa., gained ground.
3
The systolic/diastolic variations of the aortic sonogram were analyzed in many ways. Most often the
analysis utilized 2-point indices: the ratio of systolic
maximum to diastolic minimum of the waveform((S/D
ratio; Stuart) and the resistance index (RI) (of Pourcelot). In a few instances the 3-point pulsatility index
(PI) (of Gosling) was used because of its additional sensitivity to changes in the waveform between the maximum and the minimum. An interesting but complicated method of analysis is the frequency index profile
16.1).
Fig.
(FIP) (
A longitudinal examination of the aorta showed no
major changes in the values obtained from the thoracic
aorta during the last trimester: The peak velocity was
115.6 (앧 9) cm/s, the PI 1.96 (앧 0.31), the percentage
acceleration time 19.2 (앧 .2)%, the rising slope 25.7( 앧
5.6), and the descending slope 4.5 (앧 0.9). The same
applies to the abdominal aorta: The peak velocity was
99.5 (앧 18.8) cm/s, the PI 1.68 (앧 0.28), the percentage
300
250
38th to 42nd week of gestation
28th to 32nd week of gestation
acceleration time 19.1 (앧 3.3)%, the rising slope 29.9 (앧
4.9), and the descending slope 5.3 (앧 0.9).
The mean blood flow velocity in the aorta surely
rises between the 17th and 32nd weeks of gestation,
then remains constant until the calculated term, after
which it declines again until the 42nd week. Table
16.1
provides an overview of the most important quantitative and qualitative indices of blood flow after the 24th
week of gestation.
Table 16.1 Quantitative and qualitative blood flow indices in
the descending aorta of the fetus after 24 weeks of pregnancy.
Five groups by gestational age: 26 (24−27), 30 (28−31), 34 (32−
35), 38 (36−39), 쏜40 (40−42). TASAV: temporal average of spa-
tial average velocities. MV
Indices in the fetal
descending aorta
Pulse rate per min 146 143 142 145 145
TASAV cm/s2630313028
Diameter mm 3.9 5.2 5.8 6.6 7.4
Blood flow mL/min 204 400 480 638 694
Mv
max
RI 0.77 0.80 0.79 0.77 0.79
PI 1.73 1.77 1.62 1.59 1.66
cm/s 78 91 97 100 92
: peak systolic velocity.
max
Week of pregnancy
26 30 34 38 ⬎ 40
Cerebral Arteries
The prevailing state of blood flow to the brain makes
this a very important region. Vessels that may be examined include the common and internal carotid aa.,
and the arteries supplying the circle of Willis, namely
the anterior, middle and posterior cerebral as. In the
early days of Doppler ultrasound, the offset Dopplers
then in use made it much easier to analyze the carotid
aa. than thearteries of the circle of Willis. Nowadays the
latter are imaged more easily with the use of a sector
scanner with an integrated Doppler. This applies especially to the middle cerebral a., which can be displayed
in the Doppler beam at an optimal, almost 0° angle.
144
200
150
100
Mean frequency in percent
50
0
0 0.16 0.24 0.32 0.400.08
Seconds
Fig. 16.1 Normalized waveforms of the descending aorta in
the early and late third trimester: nomogram 앧 2 standard deviations. The waveform has clearly changed in the late third
trimester compared to the early third trimester. Specifically it
shows a postsystolic notch (from Griffin et al. 1983).
Mean value
Common Carotid Artery
Velocity of flow in the common carotid a. increases
throughout pregnancy. The PI declines sharply after
the 32nd week of gestation.
Middle Cerebral Artery
The waveforms of the middle cerebral a. typically display a biphasic pattern during continuous forward flow
in diastole. The values of RI in the sonogram decline
F
markedly at the end of pregnancy (
s
tudy the S/D ratio declined significantly from 6.89
(앧1.48) at 25 weeksof gestation to 4.23 (앧0.67)at term.
ig. 16.2).In another
Changes at Term and Postterm
Fig. 16.2 Values of the RI of fetal
intracranial flow curves in normal
pregnancies. The boxes correspond to the 25th and 75th percentile and include the median.
The whiskers mark the 10th and
90th percentiles for each pregnancy period (from Kirkinen et al.
1987).
100
95
90
85
80
75
70
65
60
RI in the middle cerebral a.
55
50
25–28 28–32 33 –36 37– 40 41–42
Renal Arteries
In the course of pregnancy the PI declines from the
18th to the 22nd week of gestation from 3 to 2. This
suggests a marked reduction in impedance and, hence,
possibly an increase in renal perfusion.
90th percentile
10th percentile
Weeks of gestation
Advanced Topics
Femoral Arteries
In contrast to other arterial sonograms during pregnancy the PI in the femoral aa. rises linearly from 1.8 at
15 weeks to 5.0 at 42 weeks. During the third trimester
reverse flow must be considered a normal finding.
Changes at Term and Postterm
The fetal circulation changes in many ways at the end
of pregnancy. These may be summarized by saying “we
conclude that postterm pregnancy may mimic a mild
growth restriction” (Battaglia et al. 1995).
The first report describing a deviation from what
was previously considered to be continuous development throughout pregnancy dates from 1981. Feto-
500
n = 47
400
300
200
100
Fig. 16.3 Blood flow volume in
the umbilical vein throughout
pregnancy showing the estimated
10th, 50th, and 90th percentile
(from Gill et al. 1981).
0
22 24 26 28 30 32 34 36 38 40
Blood flow volume in the umbilical vein (mL/min)
placental blood flow was observed to increase until the
36th week of gestation, reached its maximum between
the 37th and 38th week of gestation, and then declined
during the last two weeks to term. Blood flow in relation to fetal weight remained constant up to the 36th
to 37th week of gestation. After that blood flow de-
Fig.
clined (
16.3).
90th percentile
50th percentile
10h percentile
Weeks of gestation
145
Doppler Ultrasound Findings Near Term
3
The “Term Effect”
When blood flow in the fetal descending aorta was examined, a steady regression was noted after term,
while the RI remained almost unchanged. Besides the
reduction in mean flow velocity we also described a
steep decline in velocity in late systole that was so
marked in a few cases that it led to a notch in the
waveform. This phenomenon emerges about two
weeks before delivery (Fig. 16.4) and is accompanied
by significant vasodilatation. In a study of consecutive
well-established postterm pregnancies it was shown
that a notch in the waveform is normal in prolonged
16.5). At term the compliance of the
F
gestations (
aorta appeared to be reduced, in the presence of increased pulse wave velocities determined by measurement with echo markers. These aortic changes were
called “term effect.”
cm/s
100
0
Fig. 16.4 Term effect. The waveforms of the mean values of
the descending aorta are shown at one to two and three to four
weeks before delivery. In the last two weeks before delivery the
flow curve shows a distinct notch (from Vetter et al. 1989).
ig.
3– 4 weeks before delivery
1– 2 weeks before delivery
1/2 2/3
MinimumMaximum
Examination of the aortic isthmus showed that
before the 20th week of gestation the blood flow is forward throughout the cardiac cycle, and that the phase
of deceleration during diastole progresses gently and
continuously. After the 20th week a notch can be seen
at the end of systole. This increases steadily until a
brief phase of reverse flow can be demonstrated regularly at 30 weeks. Color Doppler showed that this
reverse flow in late pregnancy depends on the ductus
arteriosus. Experimental and clinical observations
have shown that increased resistance in the fetoplacental circulation first causes changes in the flow
curves of the aortic isthmus before significant changes
can be displayed in the Doppler sonogram of the
umbilical aa. The balance index (BI) is derived from the
waveform of the aortic isthmus: / (S−D)/difference of
the integral of the forward and reverse flow velocities}.
The BI gradually rises in the course of pregnancy.
T
16.2 summarizes the hemodynamic situation of
able
a pregnancy at term and postterm, as it appears in the
sonographic examination of the fetus, in particular its
large vessels.
Tale 16.2 Doppler ultrasound findings at term and beyond
The hemodynamic situation in pregnancy at and beyond
term is marked by:
Diminished placental blood flow
Unchanged or diminished impedance in the umbilical
arteries
Increased impedance in the femoral arteries
Diminished impedance in the renal arteries
Diminished mean blood flow velocities in the distal aorta
Increased pulsatility with notch as a normal finding in the
descending aorta
Diminished impedance in the aorta
Reversed diastolic flow in the aortic arch and increased BI
Increased diastolic blood flow velocities in the cerebral
arteries
146
cm/s
100
0
1 s
Fig. 16.5 Waveform of the descending aorta with a distinct
notch (arrow) in diastole in a prolonged pregnancy (from Malcus et al. 1991).
The Circulatory Balance
The pulsatile blood flow reflects a simplified model of
the driving forces of the heart on one side and the restraining forces of the peripheral resistance on the
other. Contributing factors are:
왘 The compliance of the vascular wall,
왘 The effect of dividing vessels,
왘 In particular the differences between the im-
pedances and flow resistances in the dependant
vascular beds.
Hence the sonogram of a vessel represents the balance
between all these factors.
During a normal pregnancy the placenta is the re-
gion with the least flow resistance; the cerebral aa. are
next. Based on the assumption that the combined cardiac output is stable, differential distribution of the
blood will follow the path of least resistance. Hence the
major part of the blood will be steered to the placenta.
At the end of pregnancy the demands of the brain increase in relation to the other organs. The circulation
may be redistributed—in this case to the brain with its
increased demands for supply—by opening the barriers to the brain. This is accomplished by a reduction
in the vascular resistance in the cerebral aa. However,
the increased blood supply to the brain must not occur
at the expense of the placenta. Since blood flow to the
placenta cannot be regulated directly, additional redistribution—in this case to ensure blood supply to the
placenta—can be accomplished by excluding other peripheral circulatory be ds by increasing their resistance.
A relevant example is the considerable increase in impedance of the arteries to the lower limb. Both mechanisms, opening and closing of barriers, can be observed
at term. The end result is a redistribution of the circulation to the brain without reduction in the placental
supply.
These redistributing mechanisms lead to considerable changes in the vascular links between the parallel
circulations supplied by the two chambers of the heart.
This point of division is located in the aortic arch and
16.6). Normally blood
functions like a watershed (
in the aortic arch flows forward, but near term Doppler
ultrasound has repeatedly demonstrated notches in
the waveform and reverse phases. These partial or
complete shifts are the result of either increased peripheral resistance in the aortic bed or reduced resistance in the cerebral circulation, or both.
At term many changes occur within a few days. A
few findings mimic serious disturbances in the pregnancy, making evaluation more than normally difficult. Not all changes occur simultaneously, as might be
Fig.
Clinical Conclusions
ab
Advanced Topics
cd
Fig. 16.6 Diastolic flow pattern in the aortic isthmus with consideration of placental flow resistance. (a) Initial state, (b) Slight
increase, (c) Moderate increase, (d) Severe increase (from
Teyssier et al. 1993).
expected from the observation of individual cases. Our
current understanding is too limited to draw simple
conclusions from unexpected results, especially regarding changes in the aorta. Hence, before conclusions can be drawn from the results of Doppler ultrasound examinations, all available information should
be collected and interpreted from a broad physiological and pathophysiological knowledge base.
The most important difference between the changes
at term described above and pathological changes in
the placenta is that in an unremarkable pregnancy at
term normal fetoplacental blood flow continues.
Clinical Conclusions
As noted previously, Doppler ultrasound enables us to
evaluate the condition of the fetus in chronic placental
insufficiency and to predict its future development.
Doppler ultrasound cannot evaluate risk in acute
changes such as an impending abruption or umbilical
cord loops around the neck. Since placental insufficiency near term or postterm is usually not chronic but
acute, these theoretical considerations suggest that
Doppler ultrasound cannot assist in evaluating fetal
risk. This is confirmed by clinical experience.
Doppler ultrasound is implemented to distinguish
between a compensated and a decompensated condi-
tion when biological measurements have demonstrated placental insufficiency, i.e., growth restriction.
As a rule this diagnostic procedure is initiated at a time
in the pregnancy when the infant is still immature. If
true placental insufficiency is present, most often the
pregnancy terminates before 40 weeks are completed,
and if abnormal Doppler readings are obtained from a
growth-restricted infant, it is most unlikely that the
calculated delivery date will be attained anyway.
Hence allowing a pregnancy to reach 38 weeks of gestation or the expected date of delivery is a positive
choice. This includes primarily infants with normal in-
147
Doppler Ultrasound Findings Near Term
3
trauterine development or infants above the 4th percentile of growth, in whom an abnormal Doppler f inding is not to be expected.
Once the expected date of delivery has passed, a
relative placental insufficiency must increasingly be
expected. So far no method has been found to predict
or estimate the point in time when such a relative
placental insufficiency supervenes. Of course this
raises the question of whether Doppler ultrasound can
contribute to obstetric management in this respect,
i.e., whether Doppler ultrasound can diagnose this
“physiological” placental insufficiency, similar to the
way it contributes to the diagnosis of placental insufficiency in the third trimester.
Since labor is as a rule induce d at the end of the 42nd
week of gestation, reports primarily cover this period.
According to studies by Jörn et al (1993), Arduini et al.
(1990), and Schulman et al. (1984), the tendency for
the normal values in the fetal peripheral vessels and
the umbilical aa. to decline continues after the calculated date of delivery.
In order to determine the normal values around the
calculated date of delivery, we performed daily examinations on a population of normal pregnant women
between 10 days preterm and 10 days postterm. On
average the RI increased slightly in the aorta and the
umbilical aa. Since a large number of these pregnant
women delivered during the course of the study, we
were able to show that the mean values of the RI in the
fetal aorta and umbilical aa. increased slightly a few
days (a mean of four days) before delivery, but remained within the normal range, while the RI in the
cerebral vessels declines at this time. No change was
demonstrated in the uterine vessels. All the infants had
a normal fetal outcome. The development noted in the
Doppler parameters might therefore be the expression
of a relative—physiological—placental insufficiency.
A number of research groups examined absolute
velocities in the fetal aorta and found decreased blood
flow velocities, as might be expected physiologically
from the increased aortic diameter (Battaglia et al.
1991, Rightmire and Campbell 1997, Vetter et al. 1989).
However, absolute velocities are not determined in the
course of routine diagnosis.
As noted above, Vetter described a “term effect” in
the fetal aorta (Vetter et al. 1989, Vetter 1991). This refers to a postsystolic notch in the waveform, which appears a few days before term. Swedish studies confirm
this phenomenon (Malcus et al. 1991). Admittedly, its
appearance has no diagnostic significance. Rather, the
effect is evidence of a complex redistribution of the
circulation that occurs toward the end of pregnancy,
associated with an increase in the diameter of the
aorta and an increase in diastolic flow in the cerebral
aa. It is not clear if the trigger for this change is the increased flow resistance in the systemic fetal circulation, or if the prime mover is an active reduction in
flow resistance in the cerebral aa..
In contrast to the third trimester results, which indicate that fetal risk can be predicted with relative confidence by Doppler examination, Jörn et al. (1993) found
that when the cardiotocogram (CTG) was abnormal,
Doppler ultrasound predicted fetal asphyxia or
delivery by cesarean section due to threatened fetal
asphyxia with a sensitivity of between 7.7% and 40 %,
and a positive predictive value of between 9.8% and
40%. Hence it was not possible reliably to predict risk
to the fetus after term. The conclusion is that in cases
without known risk factors Doppler ultrasound cannot
contribute materially to obstetric management when
planning the best time for delivery after the calculated
date of delivery.
148
Doppler Ultrasound during Labor?
According to Schneider (1994) the CTG during delivery
shows 50 % false positive readings. When CTG patterns
are ambiguous or abnormal, fetal scalp blood analysis
(FSBA) is therefore recommended. However, this procedure is invasive and cannot always be accomplished,
especially in the early first stage. For this reason Doppler ultrasound has been tried repeatedly to close certain diagnostic gaps.
A hint toward this end was found when relating a
highly abnormal Doppler reading before delivery, such
as zero flow in the umbilical aa., with acidosis in
umbilical cord blood. A Doppler finding less abnormal
than zero flow could not be linked to fetal acidosis. This
is understandable given the consideration that zero
flow is not brought about by acidosis. On the contrary,
only a more lasting redistribution of the circulation in
the infant leads to the noted zero flow, and then secondarily to acidosis.
Moreover, when considering the use of Doppler ultrasound before delivery consideration must be given
to the fact that contractions can change the distribution of blood flow in the fetoplacental unit.
In animals redistribution of the circulation caused by
hypoxemia and leading to decelerations in the CTG can
be displayed by Doppler ultrasound. Clinically Doppler
ultrasound can detect a peripheral rise in vascular resistance with simultaneous decline in central vascular
resistance on average two weeks before the abnormal
Summary
CTG. Schneider (1994), on the other hand, found that
there was no assured link between pathological flow
patterns in the umbilical a. and acidosis in labor. As expected, therefore, they point to the CTG and fetal blood
analysis as the most suitable methods for determining
acidosis in labor. Any decision to resort to operative
delivery because of threatened hypoxemia should
therefore be made on the basis of the CTG, not Doppler
sonographic findings.
Although Doppler ultrasound is not the most suitable method for diagnosing acidosis before delivery, it
can, if applied before delivery, assist in estimating the
Summary
Toward the end of pregnancy a possible discrepancy
between the needs of the fetus and the supply to the
placenta is adjusted by redistribution of blood flow to
the placenta—by raising the peripheral resistance in
the lower half of the body—and to the brain—by reducing the impedance in the cerebral vessels. The results
of these mechanisms can be seen in the affected vascular regions or in all parts of the central vessel, the aorta.
Hence the “term effect” in the aorta is the end result of
all these mechanisms of redistribution taking place in
the arteries to the extremities, the kidneys, or the
brain.
Using Doppler ultrasound the obstetric attendant
can detect fetal risk prospectively during the third
trimester, though this is no longer the case immediately before delivery. Hence there is no indication for
the use of Doppler ultrasound immediately before
delivery, at delivery, or in cases of postmaturity. At
reserve available for the process of parturition. The evidence for this is that infants with zero diastolic flow in
the aorta or the umbilical aa. most often cannot
tolerate vaginal delivery, and must be delivered by cesarean section on the basis of the CTG.
Doppler ultrasound is thereforean outstanding diagnostic tool and at times a predictor of risk that can be
used to capture chronic changes and draw prospective
conclusions about the remaining course of the pregnancy. However, it cannot indicate acute changes that
might supervene postterm or during labor.
Advanced Topics
these stages a CTG is surely a better instrument for
fetal monitoring.
However, since in most cases the actual delivery date
cannot be estimated prospectively, Doppler ultrasound
loses its importance as early as after the 38th week of
pregnancy. This assertion also rests on the fact that a
pregnancy found to be abnormal by Doppler ultrasound most often does not attain such a late stage.
Placental insufficiency that elicits an abnormal Doppler finding on the fetal side is usually detected early
and as a rule leads to the need to terminate the pregnancy prematurely. Hence the use of Doppler ultrasound on or after the calculated date of delivery is not
justified, since at that time acute changes cannot be
detected by this means, while normal Doppler findings
may lull the obstetric attendant into a false sense of
security.
149
3
150
17 Diagnostic and Clinical Significance of Doppler Ultra-
sound in Obstetrics
Doppler ultrasound is a noninvasive method of examining blood flows. In obstetrics Doppler ultrasound
is used chiefly to study the uteroplacental and fetoplacental vessels, but it is also used to examine the vessels of the fetus itself. The examination in these cases is
applied to flow patterns and to Doppler indices that
are derived from the flow curve and are not dependent
on the insonation angle (Evans et al. 1989, Gonser
1989, Vetter and Gonser 1992). In cardiac anomalies
and disturbances of cardiac rhythm in particular, quantitative studies of ongoing aortic perfusion and Doppler echocardiography may be performed.
In recent years numerous studies have shown a significant link between an abnormal Doppler finding and
an abnormal outcome of a pregnancy. Consequently,
Doppler ultrasound has been increasingly integrated,
but perhaps prematurely, into the diagnostic workup
of the condition of the fetus and clinical management
(Divon et al. 1989, Dornan and Harper 1994, Low 1991,
Visser et al. 1991). Two questions should be asked
before making a major commitment to Doppler ultrasound in pregnancy: firstly, whether Doppler ultrasound will provide additional information about the
condition of mother and infant, and secondly, whether
the outcome of the pregnancy can be improved if the
Doppler finding is integrated into clinical management. The question concerning the additional information relates to diagnostic significance; the question
concerning the expectation of improved outcome relates to the clinical significance of the procedure.
Diagnostic significance describes the diagnostic
power of a clinical procedure (efficiency). By contrast
clinical significance describes its usefulness in clinical
management (effectiveness), taking into account its attendant risks. To examine diagnostic significance an
adequate procedure would be a purely observational
study, while the ideal procedure to test clinical significance is a prospective randomized management or intervention study (Altman 1991, Thornton and Lilford
1993).
It seems unrealistic to think that a new procedure
that is used especially in late pregnancy would improve
the outcome of the pregnancy materially. Previously introduced procedures leave little room for further improvement by the addition of newer methods.
Moreover,there areindications thatthe developmentof
pathology in a pregnancy begins as early as conception
or in early pregnancy, and that perinatal events contribute less to long-term morbidity than previously assumed (Newnham et al. 1991). Cerebral palsy seems to
be at least one instance of this, but other, less severe
neonatal defects may belong in this category (Blair and
Stanley 1988, Longo 1992, Melone et al. 1991, Naeye et
al. 1989). Hence introducing Doppler ultrasound late in
pregnancy cannot be expected to bring dramatic improvements in morbidity statistics.
Advanced Topics
Studies of Diagnostic Significance
The diagnostic significance of Doppler ultrasound in
obstetrics is measured by the reliability with which an
abnormal Doppler finding is associated or correlated
with a negative pregnancy outcome. Criteria for the
evaluation of diagnostic significance are among others
sensitivity (sens.) and specificity (spec.) together with
positive and negative predictive value. These parameters are determined in an observational study, i.e., the
Doppler finding is only observed and at this stage must
not be integrated in the clinical management (Maršál
1991, Thornton and Lilford 1993). While positive and
negative predictive values depend on the clinical
population being studied, sensitivity and specificity
are independent of this factor (Buekens and Kaminski
1988, Grant and Mohide 1982).
The literature is full of studies addressing diagnostic
significance. Hence in what follows we can only present a selection. The studies find a significant association between abnormal Doppler readings and the following pathological conditions in obstetrics: growth
restriction, dystocia, and premature delivery
(Trudinger et al. 1991), acidosis on cordocentesis (Nicolaides et al. 1988, Weiner 1990), abnormal cardiotocogram (CTG) before delivery (Dempster et al 1989),
depression and acidosis of the newborn (Bekedam et
al. 1990, Gudmundsson et al. 1990, Reuwer et al. 1987,
Soothill et al. 1993), cerebral hemorrhage, neonatal intensive care (Trudinger et al. 1991, Weiss et al. 1992),
and histopathological changes in the placenta (Giles et
al. 1985, Hitschold et al. 1992, McCowan et al. 1987)
and the placental bed (Voigt and Becker 1992).
151
Diagnostic and Clinical Significance of Doppler Ultrasound in Obstetrics
Uteroplacental Arteries
A postsystolic notch in the uteroplacental waveform in
the second trimester is due to an abnormal reflection
of the pulse wave in the spiral aa. (Adamson et al.
1989), which is presumably the result of impaired trophoblast invasion during placentation in the first half
of pregnancy (Brosens et al. 1972). According to Campbell et al. (1983) a notch is the characteristic Doppler
sonographic correlate of preeclampsia, defined as hypertension with proteinuria, and according to Fleischer
et al. (1986) the association of such a notch with dystocia or premature delivery is highly significant in hypertensive pregnant women (sens.: 87%; spec.: 95%). This
suggests that as an indicator of hypertensive complications of pregnancy the finding of a notch is clearly su-
3
perior to creatinine clearance or uric acid level.
With unilateral implantation of the placenta the incidence of preeclampsia and intrauterine maldevelopment is significantly higher than with central implantation (Kofinas et al. 1989). Our own studies show that,
if preeclampsia is already established when a unilateral placental implantation is discovered, the contralateral Doppler findings in the uteroplacental bed
are significantly associated with the clinical and metabolic condition of the newborn (sens.: 70%; spec.:
75% for a 5-minute Apgar 쏝7, pH[umbilical a. (UA)]
쏝7.15, or base excess (BE)[UA] 쏝−8 mmol/L). According
to Thaler et al. (1992) pregnancies with hypertension
쏜140/90that also show a contralateral notch lead with
significantly increased frequency to fetal maldevelopment, cesarean section for an abnormal CTG, and longlasting neonatal intensive care.
In contrast to these studies performed on high-risk
pregnancies, Steel et al. (1990) conducted screening
examinations of the uteroplacental circulation at 18
and 24 weeks of gestation. Abnormal Doppler findings
on both occasions were followed by an increase in risk
for subsequent hypertensive complications of the
pregnancy, for example, the risk for hypertension increased from 5 % to 25%, for preeclampsia from 1% to
10%, and for intrauterine growth restriction (IUGR)
from 7 % to 27 %. Harrington et al. (1991) in a screening
study using a comparable protocol found preeclampsia
as a sequela with a sensitivity of 76% and a specificity
of 96 %. These studies suggest that it would be reasonable to screen patients with a clinically unremarkable pregnancy for the risk of later hypertensive complications of pregnancy.
Umbilical Arteries and Other Fetal Vessels
Umbilical Arteries and Fetal Aorta
According to Trudinger et al. (1986) the prenatal Doppler findings are associated with dystocia and depression of the newborn more strongly than the prenatal
CTG (CTG-NST [nonstress test]: sens.: 36%; spec.: 88%;
Doppler: sens.: 60%; spec.: 85 %). The results of Schulman et al. (1989) were even more significant for an association with later decelerations of the CTG, acidosis,
low 5-minute Apgar scores and neonatal intensive care
(CTG- NST: sens.: 7.6%; spec.: 97%; Doppler: sens.:
50%; spec.: 96%). Yoon et al. (1992) compared Doppler
ultrasound of the umbilical aa. with a biophysical profile in a high-risk population who had an elective primary cesarean section. Both methods were highly significantly associated with the pH in the umbilical aa.,
and Doppler ultrasound achieved a somewhat higher
proportion of hits (sens.: 86 % vs. 64 %; spec.: 96 vs.
90%). However, this conclusion has been questioned by
other authors. Weiss et al. (1989) compared Doppler
sonography of the umbilical aa. with the oxytocin challenge test (OCT) in IUGR, looking at their association
with the frequency of cesarean section for abnormal
CTG changes and the frequency of low Apgar scores
and low pH values in the neonate. Doppler ultrasound
detected the indicated risks before the OCT, sensitivity
and specificity being high in both methods.
End-diastolic block in the umbilical aa. of a growthrestricted fetus is one of the most reliable warning
signs of threatened hypoxemia, defined by subsequent
intrauterine fetal death or pathological CTG changes
followed by cesarean section (sens.: 77 %; spec.: 100 %)
(Reuwer et al. 1987). This finding is confirmed by the
fact that in a high-risk pregnancy end-diastolic block is
significantly associated with prenatal hypoxia and
acidosis despite primary cesarean section (sens.: 78%
vs. 90%; spec.: 98 % vs. 92 %) (Tyrrell et al. 1992).
Doppler ultrasound is suitable for perinatal prognosis of IUGR and other risks of pregnancy, but it is not
suitable for screening to detect IUGR. For this fetometry is a far superior routine procedure (Beattie
and Dornan 1989, Bekedam et al. 1990, Berkowitz et al.
1988,Bruinse et al. 1989, Burke et al. 1990,Dempster et
al. 1989, Maršál 1991, Reuwer et al. 1987, Soothill et al.
1993).
The Umbilical Vein in Arterial Diastolic Block or Reverse Flow
152
An abnormal Doppler finding in the umbilical a.
precedes abnormal CTG changes by a few days to
weeks (Schmidt et al. 1993). This interval appears to
diminish with increasing gestational age (Bekedam et
al. 1990) and when an end-diastolic block is already
Studies of Clinical Significance
present (Arabin et al. 1988, Reuwer et al. 1987, Rochelson et al. 1992, Schmidt et al. 1991). When pulsations
in the umbilical v. then supervene, sporadic late decelerations can be demonstrated just a few days later (Arduini et al. 1993).
Pulsations in the umbilical v. are an expression of
pathological changes in the central hemodynamics of
the fetal heart and in the inferior vena cava (IVC) (Lingman et al. 1986, Reed et al. 1990,Rizzo et al. 1992). They
areassociated with greatermortality than end-diastolic
block by itself (Indik et al. 1991). Pulsations in the
umbilical v. presageimminent conversionof an end-diastolic block into reverse flow in just zero to three days
(Gonser 1992). Diastolic reverse flow is the most extreme pathology in the flow pattern of the umbilical a.
and when compared with end-diastolic block is associated with a distinctly higher perinatal mortality of
about 40% to 75% (Brar and Platt 1988, Gonser et al.
1993, Mandruzzato et al. 1991, Schmidt et al. 1991).
Cerebral Arteries and Redistribution of the Circulation
Examinations of the cerebral vessels by Doppler ultrasound reveal signs of the type of oxygen sparing switch
postulated by Saling in the early 1960s on the basis of
observations in clinical obstetrics (Saling 1965, 1966,
1970), and examined concurrently by several groups in
animal models (Assali et al. 1962, Campbell et al. 1967,
Dawes 1962) and later confirmed (Bocking et al. 1988,
Cohn et al. 1974, Jensen 1989, Jensen et. al 1987, Peeters
et al. 1979, Richardson et al. 1989). Admittedly, an oxy-
gen-sparing switch cannot be detected by Doppler ultrasound directly. Only the accompanying redistribution of the fetal circulation favoring the brain shows
Doppler sonographic correlates (Arabin and Saling
1987, Arbeille et al. 1987a, Arbeille et al 1987b, Maršál
et al. 1984, Wladimiroff et al. 1986). The combination
of a marked flow disturbance in the aorta and the
umbilical a. with an abnormally increased diastolic
flow only in the cerebral aa. can be interpreted as a redistribution of the circulation (Vetter 1993). Such a
Doppler sonographic constellation, when found with
IUGR, is associated with the outcome of the pregnancy
(Arbeille et al. 1987b, Arduini et al. 1992, Gramellini et
al. 1992).
In pregnancies in which cesarean sections are performed for severe growth restriction or severe preeclampsia, the expected neonatal hypoxemia was detected earlier and with greater accuracy by antepartal
Doppler sonography of the middle cerebral a. (MCA)
than by computer-aided antepartal CTG analysis
(Chandran et al. 1993). This finding is predictably confirmed by the fact that in severe growth restriction
there is a significant correlation between fetal hypoxemia determined by cordocentesis and abnormal Doppler findings in the MCA, with the exception of false
positive normal Doppler readings in the most severe
cases of fetal hypoxemia (Vyas 1990). In fetuses with
the most severe growth restriction (쏝 1st percentile)
an apparent terminal normalization of previously
highly abnormal cerebral Doppler readings has been
observed (Chandran et al. 1993, Erz and Gonser 1995,
Mari and Wassersturm 1991). The cause of this might
be the development of cerebral edema with increased
intracranial pressure (Vyas et al. 1990), but it is more
likely that it is a terminal breakdown of the compensatory centralization of the fetal circulation (Arduini et
al. 1992, Weiner et al. 1994). This mechanism was
elucidated in acute (Jensen et al. 1987) and chronic (Richardson et al. 1989) animal models. Hence such secondary “normalization” of cerebral flow patterns must
be regarded not as an improvement, but rather as a terminal deterioration of the condition of the fetus.
Advanced Topics
Studies of Clinical Significance
Taken together the above-mentioned observational
studies show a distinct link between the results of
Doppler ultrasound and the outcome of a pregnancy.
However, for methodological reasons it is not possible
to conclude that this information can improve the outcome of the pregnancy. This question is addressed by
the study of clinical significance, which investigates
whether Doppler ultrasound can lead to directions for
management that can improve the course and result of
obstetric care. However, this question can only be answered by studies including clinical management and
interventions. In such studies patients are allocated
randomly to two treatment groups. In one group treatment follows conventional criteria (control group),
while in the other group management is modified by
Doppler sonographic criteria (Doppler group) (Altman
1991, Buekens and Kaminski 1988, Giles and Bisits
1993, Maršál 1991). Thus, the intervention consists of
the integration of Doppler findings into obstetric management.
Compared to the number of observational studies of
diagnostic significance there are considerably fewer
prospective randomized intervention or management
studies addressing clinical significance (Table 17.1).
Unfortunately, no standardized management protocol
was integrated into the design of the interventional
studies. Rather, the responsible clinician was asked to
incorporate the Doppler findings according to his/her
153