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Multiple Pregnancy and Doppler Ultrasound
Studies Using Doppler Ultrasound for Multiple Pregnancies
124
Monitoring multiple pregnancies by Doppler ultrasound was considered promising from a relatively
early stage. Selective display of hemodynamic parameters was especially well accepted, since, as mentioned
earlier, the simpler methods for assessing risk in single
pregnancies are often ineffective in multiple pregnancies.
Consequently, some studies were undertaken as
early as the 1980s using Doppler ultrasound examinations for screening, but also to evaluate previously established risks. However, diagnostic studies of the fetal
membranes to determine chorionicity for the assessment of risk, which have been especially valuable
lately, were not yet as developed when those studies
2
appeared.
In 1985 Giles et al. published the first larger study of
the use of Doppler ultrasound in 76 multiple pregnancies. They examined the S/D ratio (the ratio between
the systolic maximum [S] and the diastolic minimum
[D] of the waveform) in the umbilical aa.. Abnormal
elevation of the S/D ratio identified growth-restricted
fetuses in 26 out of 33 cases, while normal values were
found in all 32 pregnancies in which the infants were
of normal size. The sensitivity was 0.79; the specificity
1. By contrast, the early results from studies linking
discordant growth with presumed TTTS were rather
anecdotal in nature.
Giles et al. (1993) investigated whether factors interfering with growth were preplacental or placental.
They were able to show that when Doppler findings in
a twin were abnormal and growth was restricted this
was accompanied by selective placental pathology. In
these cases they did not see this as a sign of preplacental pathology, as might be assumed in single pregnancies with growth restriction and abnormal Doppler
findings in the maternal uterine aa.
In 1987 Nimrod et al. published a study designed to
find indicators for an unfavorable course for a pregnancy. They determined the S/D ratio in the umbilical
aa. and the descending aorta together with the pulsatility index (PI). They also determined flow volumes
in the aorta. In summary, their results showed that
some individual readings as well as the indices, especially flow volume, were of almost identical value in
predicting an unfavorable outcome of the pregnancy.
The sensitivity was 0.50; the specificity 0.89. Doppler
ultrasound was considered to be a very promising addition to the armamentarium.
Gerson et al. (1987) conducted a Doppler study on 52
twinpregnancies and foursets of tripletsdesigned todiagnose discordant growth in twins as early as possible.
The result was a fairly good predictive value,which was
not possible by other methods. The sensitivity was0.82;
the specificity 0.98, with a high kappa of 0.82.
Saldana and co-workers (1987) chose a rather complex approach. They tried to register differences in the
S/D ratio 쏜0.4 in 69 twin pregnancies and to find
differences in weight of 쏜350 g in the third trimester
between the pairs of twins. The outcome was disappointing, resulting in a predictive value of 0.42. On the
other hand, the predictive value for a normal weight
when the S/D ratio was 쏝0.4 was much more favorable
at 0.91.
The first such study was attempted by Farmakides et
al. (1985), who investigated 43 twin pregnancies. They,
however, calculated a sensitivity of 0.73 and a specificity of 0.82. The question that arises for both studies
is whether the selected approach, namely looking for
differences by pairs, is practical.
The influence on clinical management and perinatal
data of Doppler ultrasound examination of the umbilical aa. between the 28th and 32nd weeks of gestation
was addressed by Trudinger’s group (1988). Revealing
the results of the Doppler examination to the attending
physicians in the test group, while for a control group
Doppler data were simply collected under blind conditions, showed a distinct reduction in perinatal mortality, fetal deaths, and utilization of neonatal intensive
care.
In 1990 the same working group found a similarly
convincing result in triplet pregnancies, with a close
link between changes in the Doppler sonogram of the
umbilical aa. and developmental delays in individual
triplets.
Hastie et al. in 1989 found the results of Doppler ultrasound less convincing. They examined the umbilical
aa. in 89 twin pregnancies at monthly intervals and
found a sensitivity of 0.29 at a predictive value of 0.34
for growth restriction.
Divon et al. in 1989 examined 58 twin pregnancies in
the third trimester. They found that the 18 discordant
fetuses could not be detected in all cases with any of
the methods they used, including Doppler sonography
of the umbilical aa. A positive predictive value of 0.73
and a negative predictive value of 0.90 were only
achieved by a combination of biological measurements
and Doppler ultrasound.
In 1991 Gaziano et al. arrived at the conclusion that
Doppler ultrasound can make a valuable contribution
to the monitoring of multiple pregnancies when they
examined pregnancies involving 94 pairs of twins and
seven sets of triplets.
In a prospective longitudinal study in which he examined not only the umbilical aa. but also the internal
carotid aa. Degani demonstrated the usefulness of
Doppler ultrasound in detecting risk factors early on
(Degani et al. 1988, Degani 1990). They calculated a
positive predictive value of 0.91 and a negative predic-
blubber
Studies Using Doppler Ultrasound for Multiple Pregnancies
tive valued of 0.91, with a sensitivity of 0.83 and a
specificity of 0.95 for a PI (PI after Gosling) of 쏝1.2 for
the internal carotid a. In 1992 Degani et al. calculated
that growth restriction could be diagnosed by Doppler
ultrasound on average 3.7 weeks before biometric
measures. Admittedly, with a sensitivity of 0.58 and a
positive predictive value of 0.71 the reliability was far
from perfect. Here, too, the sensitivity was improved to
0.84 by combining the technique with biological measures.
In 1992 Kurmanavicius et al. examined 32 pairs of
twins for growth restriction and discordant growth. A
change in the resistance index (RI) of 0.1 attained a
sensitivity of 0.78, a specificity of 0.96, a positive predictive value of 0.88, and a negative predictive value of
0.92. These results led to the recommendation that
Doppler ultrasound should be incorporated in the
management of multiple pregnancies.
According to Jensen (1992), Doppler examinations of
twins one week before delivery, found that an elevated
RI (RI of Pourcelot) indicated impairment of placental
supply both in nutrition, with consequent lower birth
weight, and in respiration, with late slowing of the
CTG.
Beyond this Jensen (1993) examined the association
between the results of Doppler ultrasonography of the
umbilical aa. and a difference of 쏜0.1 kPa between the
of multiple gestations at delivery. For a RI 쏜75 the
pO
2
positive predictive value was 0.64 and the specificity
0.78.
Comparing the systolic/diastolic variability of the
flow curves in the umbilical aa. between normal
singletons and twins, Shah et al. (1992) were able to
show that, in a growth-restricted twin the indices rise
in the course of the pregnancy instead of declining in
the usual way.
In 1993 Grab et al. examined blood flow in the uteroplacental as well as the fetoplacental aa. with a view to
observing the development of growth restriction. The
success rate was moderate, even when only the last
readings before delivery were selected. Sensitivity was
0.60, specificity 0.66, postive predictive value 0.33, and
negative predictive value 0.85.
Similarly the results of Faber et al. (1995) sound less
positive. They examined the value of Doppler sonographic screening in twin pregnancies in relation to
obstetric results. They examined the uterine aa. to
evaluate the uteroplacental circulation, the umbilical
aa. to estimate the fetoplacental circulation, and the
descending aorta and middle cerebral a. to evaluate the
fetal circulation. They were able to demonstrate that
the values did not differ from those of singleton pregnancies. They constructed scores—for the Doppler
finings as well as for the outcome of the pregnancy and
the infant’s condition after delivery—and then looked
for correlations. With a sensitivity of 0.25 and a specificity of 0.63, the result was considered inadequate for
screening.
Echocardiography, with the determination of flow
velocities in the inflow and outflow tracts of the heart,
has been of little help to date, perhaps because of the
variety of causes of growth restriction (Rizzo et al.
1994).
able
T
12.1 shows the associations described in the
literature between the findings by Doppler ultrasound
and “fetal outcome.”
In summary, most studies indicate that especially
nutritional impairment in twin pregnancies can be detected earlier with Doppler ultrasound than by other
methods, and that risks can be reduced or controlled
by the application of Doppler ultrasound and appropriate management.
Theoretical Considerations Related to the Above Studies
What were the investigators expecting to discover?
For a start it is clear that in a dichorionic as well as a
monochorionic twin pregnancy impairment in the
uteroplacental blood supply can lead to lack of adequate nutrition in both infants, but is unlikely to do so
selectively in one fetus. Hence discordant growth cannot be assessed by examination of uteroplacental
blood flow.
Obstetric Applications of Doppler Ultrasound
Table 12.1 Correlations between Doppler ultrasound findings and clinical outcome described in the literature. (+: positive correlation; −: no correlation. UA: umbilical arteries, ICA: internal carotid arteries, MCA: middle cerebral aa., PL hist: placental histology,
IUGR: intrauterine growth restriction.
Uterina a. UA Aorta ICA MCA Pl hist
Discordant growth (IUGR) − + +
Unfavorable outcome + + +
Intrauterine death +
Placed in intensive care +
Perinatal mortality +
Respiratory failure (CTG) + +
blubber
125
Multiple Pregnancy and Doppler Ultrasound
2
Analysis of fetoplacental blood flow in a dichorionic
pregnancy provides selective information about the
blood supply to a single fetus. Hence analysis of systolic/diastolic variability should detect those fetuses
whose villous circulation is qualitatively impaired.
However, fetuses with an insufficient blood supply
cannot be detected using this method, because placental areas or volumes are too small. To identify them,
quantitative studies of absolute velocities or flow
volumes are needed, and such measurements were not
taken in the studies mentioned above.
In monochorionic twins the fetoplacental conditions
are much more complex, and they can rarely be evaluated with any degree of confidence. This is due to the
almost obligatory anastomoses, which make the selective evaluation of the supply to one individual almost
impossible.
The fetal circulation offers many opportunities for
analyzing the supply situation or its consequences.
Originally the main vessel analyzed was the descending aorta, from which conclusions about cardiac
output, the peripheral circulation, and the efficiency of
the placenta were derived. However, it is simpler to interpret readings from vessels that supply only a single
region, such as the cerebral vessels, the coronary vessels, or the renal vessels. For instance, the cerebral
circulation can be expected to reveal redistribution of
the blood supply to the brain in the presence of impaired respiration. Unfortunately, the same changes,
namely an acceleration of diastolic flow velocity, may
also be seen during fetal activity and at term, so that a
direct interpretation is impossible without information about the conditions at the time of the study.
These theoretical considerations lead to the conclusion that the correlation between blood flow analysis
and actual clinical condition is not as close as is
desirable. Yet it is precisely in these complex circumstances that Doppler ultrasound can serve as a valuable
differential diagnostic tool. On the other hand, the results of the above studies are an incentive to add quantitative flow determinations.
Special Considerations for the Use of Doppler Ultrasound in Twin Pregnancies
126
Acardius Acranius, TRAP
A problem specific to multiple pregnancy is the partial
or complete vascular supply from an acardius acranius
to a healthy twin. In such a case umbilical blood flow is
reversed (TRAP). One heart supplies two circulations
and therefore decompensates relatively early (Donnenfeld et al. 1991). In such cases a decisive diagnostic
role is played by spectral and also color Doppler (Benson et al. 1989, Kirkinen et al. 1989, Shalev et al. 1992,
Ishimatsu et al. 1993, Hecher et al. 1996).In a few cases
a rudimentary autonomous circulation may be found
in the acardius, and this might prevent decompensation in the healthy twin.
Crossed Cord Around the Neck
Another specific complication of monoamniotic twins
is a cord looped around the neck, where one twin endangers the other. Even though therapeutic measures
are of no clear value in this situation (Peek et al. 1997),
the presence of the complication must be ascertained
for appropriate considerations. Such looping of the
cord is most easily diagnosed by color-coded Doppler
sonography (Aisenbrey et al. 1995).
Because of their length and the corresponding
damping of flow resistance, the flow waveform in the
umbilical aa. is usually “smooth.” Obstructions such a
knot in the cord disturb this picture, so that an early diastolic notch appears (Jakobi et al. 1994). This change
may also be found in multiple pregnancies, where intertwined cords (Abuhamad et al. 1995) are a clue for
complications.
Another complication is compression of the umbilical v., which can be detected by color Doppler ultrasound by its clearly elevated flow velocity (Belfort et al.
1993).
Velamentous Insertion and Vasa Previa
Insertion anomalies and vasa previa are more common
in monochorionic multiple pregnancies than in dichorionic multiple pregnancies and in singletons
(Vogel1995). For this reason a search for this complication can be targeted in monochorionic multiple pregnancies. It can be displayed by color-coded Doppler ultrasound.
blubber
Special Considerations for the Use of Doppler Ultrasound in Twin Pregnancies
Monochorionic Multiple Fetuses with Circulatory Communication Disorders
Communication between the circulations of monochorionic twins is probable. Superficial anastomoses
on the chorionic plate visible to the naked eye may be
artery-to-artery, vein-to-vein or, very rarely, artery-to-
vein. Artery-to-vein communication is usually indirect
or deep connections through capillaries in divided
cotyledons, forming the so-called third circulation.
Connection of an artery-to-artery anastomosis to a
divided cotyledon was formerly considered to be one
of the most important types of communication (Arts
and Lohman 1971). In most cases the communication
is balanced and poses no problem to the fetus. In a few
cases growth discordances may occur independent of
communication.
In one study of 23 monochorionic placentas anastomoses were found in 20. A total of 14 different types of
communication were described in this study. In three
cases a FFTS was found (Arts and Lohman 1971).
In another study 20 monochorionic placentas were
examined. Ten of these were the basis of a TTTS. These
10showed significantly fewer anastomoses. In seven of
them only deep artery-to-vein anastomoses were seen
(Bajoria et al. 1995). On the basis of this finding the
authors concluded that twin-to-twin transfusion
might originate in a lack of balancing anastomoses. Superficial anastomoses enable blood flow in both directions, allowing unbalanced flows that are due to deep
artery-to-vein anastomoses to be balanced. The clinically unfavorable developments occurred when
neither artery-to-artery nor vein-to-vein anastomoses
were present (Machin et al. 1996).
These anastomoses have long been demonstrated by
ultrasound imaging and Doppler (Erskine et al. 1986).
Their detection has been made somewhat easier since
the development of color-coded Doppler ultrasound
(Donner et al. 1995, Hecher et al. 1995).
condition improved, the previously elevated PI
decreased again (Dohno et al. 1994). In a few cases it
was possible to display the interference by showing
the interference caused by opposing waves at the
artery-to-artery anastomoses in the common circulation (Hecher et al. 1994). Differences in renal perfusion, determined by Doppler ultrasound, are closely
associated with differential production of urine in the
twins (Mari et al. 1993).
The clinical course and the stages of decompensation and recompensation can be followed by Doppler
ultrasound, especially if the central circulation is
monitored. An early diastolic notch, a diastolic block as
long as a block throughout diastole, and even reverse
flow may develop in the donor. Preload and afterload
are increased in the recipient in the terminal phase. It
is possible to display signs of cardiac insufficiency that
are due to the incompetence of a dilated tricuspid
valve with regurgitation (Zosmer et al. 1994). Venous
sonograms indicate raised central venous pressure
(Rizzo et al. 1994, Hecher et al. 1995, Weiner and Ludomirski 1994), which often leads to pulsations in the
umbilical v. Abnormal blood flow in the fetoplacental
vascular bed may also be found in the recipient, especially if placenta edema has developed. If the fetus survives, it may eventually exhibit pulmonary hypertension, or a lethal cardiomyopathy with endocardial fibroelastosis (Zosmer et al. 1994). On the other hand,
the edema may remit (Achiron et al. 1992). The outcome is difficult to predict.
After the intrauterine death of one fetus, the other is
at high risk, since its counterpart is now missing. The
reactions differ greatly, for example, in about 25% of
cases the sequel is thromboembolism. The circulation
especially becomes unstable, which can be recognized
by variable flow curves (Lander et al. 1993). It may also
result in reverse feto−fetal transfusion, in which case
the surviving fetus can pump a great deal of blood into
the other fetus without receiving any return (Jou et al.
1993).
Obstetric Applications of Doppler Ultrasound
Twin-to-Twin (Feto−Fetal) Transfusion Syn-
drome (TTTS, FFTS)
Some of the contradictory reports may be due to a lack
of precision in the diagnosis, since this was not clear in
all the cases described in the literature. Some authors
reported contradictory findings (Blickstein 1990, Yamada et al. 1991), while others could not distinguish
between donor and recipient on the basis of Doppler
ultrasound data from the umbilical aa. (Dickinson et al.
1995, Pretorius et al. 1988, Giles et al. 1990a).
Nevertheless, some of the Doppler findings of these
studies will be presented here. A major difference in
the PI of the umbilical aa. of the two fetuses was found
before the development of hydrops fetalis. When the
blubber
Hydramnios-Oligohydramnios
Hydramnios-oligohydramnios is a descriptive term for
twins with discordant findings, the principal symptom
of which is inequality of amniotic fluid. This phenomenon has interested obstetricians for manyyears (Schatz
1882 and 1900). With the advent of Doppler ultrasound it seems to become more and more feasible to
work out its causes in individual cases. In many,
though not in all, cases the reason for uneven volumes
of amniotic fluid is a TTTS. For instance, 6 out of 33 consecutive pregnancies with polyhydramnios-oligohydramnios had a dichorionic placenta and therefore no
vascular anastomoses (Reisner et al. 1993), meaning
that there could be no TTTS. The cause of this condition
127
Multiple Pregnancy and Doppler Ultrasound
has been the subject of speculation (Vetter 1993) and
proposals have been put forward for studies that might
contribute to the solution of the dilemma posed by the
differential diagnosis. The proposal put forward by Lachapelle et al. (1997) is enticing. They suggested that
echocardiography might be used to determine
whether the smaller twin is the donor in a transfusion
syndrome, thus showing signs of a hyperdynamic
Summary
Ultrasound imaging and Doppler ultrasound are integral monitoring modalities for twin pregnancies. A
2
simplified diagram outlining our recommendations for
the introduction of these methods is shown in
12.3. Especially in the case of twin pregnancy, which is
difficult to monitor by simpler means, Doppler ultrasound is suitable for gaining an insight into the physiology and pathophysiology of this often problematic
pregnancy. Early recognition of abnormal development leads to an improved perinatal outcome. Doppler
ultrasound should not be limited to pregnancies in
Figure
circulation, or whether it is simply growth restricted,
and therefore exhibiting the same clinical picture as
the donor in a TTTS, but actually is merely receiving
marginal circulation. The most important differential
diagnosis for a twin that is, as it were, lying in a dry bed
(stuck twin) is a primary renal problem, such as renal
agenesis (Kuller et al. 1994) or a secondary renal problem due to impaired supply.
which discordant growth has already been detected,
since this method is especially suited to the early detection of discordant growth.
“Given the limitations of present knowledge, serial
assessment of twins beginning in the midtrimester
with ultrasound observation, and adding a combination of Doppler velocimetry and nonstress testing in
the third trimester, seems to represent the most reasonable current approach to twin well-being.” (Devoe
and Ware 1995)
128
10th to
12th
week of
gestation
16th to
20th
week of
gestation
24th
week of
gestation
Monitoring of multiple pregnancy
Chorionicity, amnionicity,
Dichorionic
Ultrasound
normal
+ +
Doppler of
umbilical a.
nuchal fold
Monochorionic,
diamnionic
Umbilical aa.
correspond
Doppler of
umbilical a.
Fig. 12.3 Recommended sono-
graphic diagnostic procedure in
multiple pregnancies.
Monochoronic,
monoamnionic
Umbilical aa.
entwined
–
Weekly
Ultrasound
Doppler qualitative
and quantitative
Echocardiography
blubber
13 Possible Applications of Doppler Ultrasound
in Fetal Anemia
In spite of successful anti-D prophylaxis and other
monitoring strategies, fetal anemia continues to pose a
problem for the obstetrician. New developments, especially in ultrasound, have brought major changes in diagnosis and treatment. The diagnostic process has become highly specific because percutaneous umbilical
blood sampling allows direct access to fetal blood.
Treatment is more successful than ever as a result of
intravascular transfusion, even in cases that previously
appeared to be hopeless. Thus, with sufficient experience, invasive diagnostic and therapeutic procedures make possible specific and—corresponding to
verifiable paradigms—planned and properly adjusted
procedures with a calculable risk.
Diagnostic procedures when fetal anemia is suspected involve noninvasive, and lately again more and
more invasive means. The need for accurate and reliable diagnosis, relevant for management, is opposed by
the need to keep the pregnancy intact. However,
demands for the safety of the pregnant woman are increasingly met even in invasive procedures. This is due
to technical developments, especially in sonography,
and increasing experience with invasive methods in
larger centers. In what follows we will discuss the applications of noninvasive diagnostic methods.
Noninvasive Procedures for Suspected Fetal Anemia
These include procedures that do not affect the integrity of the pregnancy:
왘 The antibody titer in corresponding blood incom-
patibilities provides a rough indication whether
problems for the fetus can actually be anticipated.
왘 The zygosity of the blood group of the partner with
respect to the relevant antigen is an indication
whether the problem is uniformly present or may
not be significant for the current pregnancy.
왘 If the cardiotocogram (CTG) shows tachycardia, a
silent type oscillation, or deceleration, this is inter-
preted as impaired oxygenation.
왘 However, ultrasound, including both imaging and
Doppler ultrasound, is the core noninvasive procedure.
Ultrasonic Imaging
Table 13.1 shows the hemodynamic consequences of
fetal anemia.
Ultrasonic imaging can determine the sequelae of
fetal anemia, including cardiac output, increased
hemolysis, or a resulting reduction in protein neogenesis. Admittedly most indicators only hint at the “true”
13.2sum-
situation and are somewhat imprecise.
marizes these indicators of fetal anemia and their
pathophysiological significance.
Table
Table 13.1 Hemodynamic consequences of fetal anemia
Cardiac output앖
− Blood flow velocity increased: heart enlarged 앖
− Vessels dilated: arterial compliance 앗
− Renal perfusion 앖: polyhydramnios
Blood viscosity 앗
Table 13.2 Indicators of conditions associated with fetal
anemia and its sequelae that may be displayed by ultrasound
imaging
Ultrasonic indicator Pathophysiological meaning
Indicator to TS-mode
ultrasound
Spleen enlarged 앖 Increased hemolysis
Liver enlarged 앖 Hepatic erythropoiesis
Heart enlarged 앖 Increased cardiac output
Intraperitoneal
volume 앖, and intestines
dilated
Pericardial effusion,
ascites, edema, or
hydrops
Polyhydramnios Increased renal perfusion due
Placental thickness 앖
Umbilical cord thickness 앖
Nonspecific signs of a severe
fetal disorder
Very serious consequences of
severe hemolysis
to increased cardiac output
Adaptation to increased blood
flow in the placental circulation
Obstetric Applications of Doppler Ultrasound
129
blubber
Possible Applications of Doppler Ultrasound in Fetal Anemia
2
Doppler Ultrasound
Through quantitative flow analysis and flow profile
analysis, Doppler ultrasound contributes to the detection of increased cardiac output.
The original studies emphasized the quantitative
analysis of placental perfusion by Doppler ultrasono-
Fig
1
graphy of the umbilical v. (
this
sons
the descending aorta. However, with improved instrumentation Doppler sonography of the umbilical v.
should see a renaissance.
Again, for technical reasons the examination of the
descending aorta has lately been replaced by that of
the middle cerebral a., though factors other than cardiac output and the quantity of oxygen carrier play a
major role in these vessels. Thus, here, too, new and
different concepts must be expected in the near future.
The parameters under discussion in the examination
of the descending aorta and the middle cerebral a. include the maximal systolic velocity (
mean flow rate over a cardiac cycle (Fig,
flo
The flow profile becomes increasingly flatter, until a
marked frequency-free spectral window is seen in systole (Fig. 13.3), especially prominent in three-dimensional analysis of the Doppler signal. The waveform occasionally presents a late systolic notch, probably
generated by reflections from the pulse wave passing
through vascular walls maximally dilated by the increased volume (
T
able
qualitative flow changes in fetal anemia that can be
displayed by Doppler ultrasound.
Noninvasive studies are primarily suited to detecting
changes in the course of fetal anemia. However, they
are not sufficiently specific as far as primary diagnosis
and quantitative study of anemia are concerned to
totally displace invasive methods from the diagnostic
armamentarium.
Apart from its diagnostic function Doppler ultrasound is also suited to monitoring treatment (
Changes such as volume expansion and loading following intravascular transfusion are the main targets of
such an investigation. Besides volume, pressure
changes also occur in the body and in the venous as
well as the arterial circulation. For instance, the pressure in the umbilical v. is raised moderately, but not
was soon abandoned in favor of examining
w volume, all of which are elevated in fetal anemia.
Fig.
13.2).
13.3 provides a summary of the quantitative and
3.1). For technical rea-
Fig. 13.2), the
13.3), and the
13.4).
Fig.
above normal values after the intravascular transfusion of a nonedematous fetus. In an edematous fetus it
is raised initially, but reverts to normal within 24 hours
after transfusion. After intraperitoneal transfusion the
pressure in the umbilical v. rises just as after intravascular transfusions. The intraperitoneal pressure
in such transfusions is lower than in the umbilical v.
In animal experiments using anemic lamb fetuses
Fig. 13.1 Ductus venosus in fetal anemia. Time average veloc-
ity (TAV) of 49 cm/s is significantly elevated.
Fig. 13.2 Middle cerebral a. in fetal anemia. V
elevated. Late systolic notch is a sign of tricuspid insufficiency.
of 79 cm/s is
max
130
Table 13.3 Doppler findings in fetal anemia
Quantitative flow changes Qualitative flow changes
Blood flow velocities 앖 Waveform showing notch
Vasodilatation 앖 Flow profile flattened
Flow volume 앖
blubber
Fig. 13.3 Doppler display in fetal anemia. Aorta; TAV at 38 cm/
s is elevated. There is a signal-free systolic window.
central venous pressure and mean arterial pressure rise
after transfusion. Administration of furosemide does
not influence this effect significantly. While arterial
and venous pressure rose, heart rate slowed after
transfusion in this experiment. Cardiac output, as
measured by the cardiac index, is raised in fetal anemia.
In summary, it may be said that Doppler ultrasound
can display the circulation changes due to excess blood
volume such as are routinely seen in chronic anemia.
However, to avoid error, interpretation of the result
must, as always, include all available diagnostic findings. It remains to be determined in the near future
whether the most suitable vessel for such an examination is the return vessel to the placenta, namely the
umbilical v., or the fetal descending aorta, which transmits a large part of the cardiac output, or even the
middle cerebral a., which is a favorite site because it
lends itself to a favorable insonating angle.
Noninvasive Procedures for Suspected Fetal Anemia
Fig. 13.4 Display of umbilical cord perfusion during intrauterine transfusion into the umbilical cord.
Obstetric Applications of Doppler Ultrasound
blubber
131
2
132
blubber
14 Umbilical Cord Complications and Doppler Ultrasound
The course and structure of the umbilical cord can, in
principle, be displayed by gray-scale ultrasonic imaging when there is sufficient amniotic fluid. However,
near term or in critical situations this contrast can be
limited, and the abdominal wall may not provide good
imaging in all pregnant women. In such cases colorcoded Doppler of the umbilical vessels makes it
possible to find the umbilical cord, especially when it is
in an unusual location, for example, looped around the
Figs.
neck (
the presenting part.
The number of vessels can be determined by gray-
scale or color-coded display.
The thickness of the umbilical cord is of great signifi-
cance, since it is a measure of the more or less abun-
14.1,14.2a, b), the extremities, or ahead of
dant supply of Wharton’s jelly. For one thing, a thick
umbilical cord is considered to be an indication of
sufficient nutrient supply for the fetus, for another the
thickness of the umbilical cord can be an indicator of
the degree of risk when there are knots or kinks in the
umbilical cord, since a thick cord is hardly in danger of
compression.
Color-coded Doppler ultrasound can also detect
knots in the umbilical cord, especially when they need
to be distinguished from false knots. Doppler ultrasound is also valuable in the detection of eccentric insertions and vasa previa. Similarly, it may be used to
make a definitive diagnosis of intertwining of the
umbilical cords of monoamniotic twins.
Obstetric Applications of Doppler Ultrasound
Fig. 14.1 Triple umbilical cord loop. Transverse cut of neck.
zontal section without color Doppler. (b) Horizontal section
with color Doppler.
컄Fig. 14.2 Display of the cord looped around the neck. (a) Hori-
Doppler Ultrasound Findings when Umbilical Cord Complications Affect Hemodynamics
As a rule the unusual findings in the umbilical cord described above do not pose an acute problem at the time
of diagnosis. In individual cases, however, spectral or
color Doppler sonography may detect a hemodynamic
dysfunction by a reduced flow in the umbilical v. or aa.
Umbilical cord knots may show a reflection phenomena in the arteries, i. e., the usually smooth waveform
blubber
of the sonogram of the umbilical aa. shows a notch
ig.
F
14.3). A constriction of the lumen of the umbilical
(
v. can be seen as a considerable increase in the flow
rate and a consequent localized color shift that may extend to aliasing in the color Doppler image.
a
b
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