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Vascular Supply of the Uteroplacentofetal Unit and Techniques for the Examination
1
ing effect) through the ductus venosus, and the foramen ovale.
The two cardiac circulations flow functionally in parallel with almost complete pressure equalization at the
level of the atria. To this end two shunts are provided:
The first, the ductus arteriosus, connects the pulmonary a. with the descending aorta. The second is the
foramen ovale, which, by connecting the left atrium
with the right, assures a shunt to the ascending aorta
ig.
F
3.8). The peripheral resistance of the vascular bed
(
Fig. 3.7 Display of the origin of the umbilical cord and the
intra-abdominal course of the vessels. Ascending from the
right: the umbilical aa. from the fetal iliac a.; descending from
above to the left: the intra-abdominal part of the umbilical cord
and the ductus venosus.
supplied by the right heart, which includes the umbilical cord and the placenta, is normally lower than that
of the left heart, which preferentially supplies the
head, neck, and upper extremities. This probably is the
reason for the greater stroke volume ejected by the
right heart than the left. The ratio of left to right has
been determined to be between 1.3 and 1.8. This ratio
may be altered by an increase in the afterload in the
descending aorta, leading to a pressure buildup with
resulting shunt obstruction or reversal.
Fig. 3.8 Display of an aortic arch with the vessels ascending
from it.
44
Methods of Examining Specific Vessels
Displaying the Maternal Vessels
The primary examination here is of the two uterine aa.
that arise from the internal iliac aa. and divide into
smaller uterine branches in the myometrium. The
uterine aa. must be examined by color Doppler, since
these vessels cannot be adequately defined in black
and white.
Examining the Uterine Arteries in the Second
Trimester:
왘 Localization: At the lower pole of the uterus in the
myometrium bilaterally.
왘 Examination technique: The uterine a. is first lo-
cated by color Doppler sonography. The transducer
is applied above the inguinal region as shown sche-
Figure
matically in
be placed relatively superficially. First locate the
iliac a. and v. with the color Doppler, then redirect
the transducer me dially to the myometrium. Usually the uterine a. will be located with little difficulty where it runs from its origin from the internal
iliac a. (Fig. 3.10) into the myometrium toward the
transducer. The transducer may also be moved in
3.9. The Doppler window must
the reverse direction, from the amniotic cavity
laterally, to display the course of the uterine a. The
characteristic Doppler waveform of the uterine a.
can then be identified from the Doppler spectrum.
The course of the uterine a. can almost always be
displayed, while the arcuate branches can as a rule
only be displayed as points (
왘 Significance: Whether the maternal blood supply is
sufficient or not after the end of the second
trimester is decided following completion of the
trophoblast invasion.
왘 Flow profile: The course of the vessels can be dis-
played by swinging the transducer medially from
the common iliac A. and V. in color mode (Fig. 3.12).
The display shows a moderately steep systolic rise
and a continuous decline to end-diastole, as well as
poor demarcation between systole and early diastole (Figs. 3.13,3.14).
왘 Reference value: A resistance index (RI) under 50 %
is normal.
왘 Abnormal findings:
— Increased resistance parameters, such a high RI,
or the persistence of certain characteristics of
the waveform, such as notching, after the 20th
week of pregnancy, indicate that the pregnancy
is at risk (Fig. 3.15).
Fig. 3.11).
왕
Fig. 3.9 Schematic demonstration of the examination of the
uterine aa.
On the left a demonstration of the potential movements of the
transducer from lateral to medial. The iliac a. is first displayed by
color Doppler ultrasound by placing the transducer above the
inguinal ligament. From the iliac a. the transducer is directed
medially. As a rule the uterine a. is then seen as a vessel running
Methods of Examining Specific Vessels
Basic Concepts
Fig. 3.10 Color display of the iliac a. with the origin of the
uterine a.
relatively high toward the transducer. It can be displayed over
its course.
On the right, the transducer is moved from medial laterally. In
this case the point of departure is the amniotic cavity. The color
window is set relatively high in the display to find and display
the course of the uterine a. in the myometrium.
a b
c
Fig. 3.11 Display of all uterine vessels from the iliac to the arcuate aa. (a) The uterine a. is displayed by spectral Doppler. The
uterine a. after its origin from the iliac a. (b) and its distal course
toward the arcuate aa. (c). (d) The anatomy of the course of the
vessels is displayed by color Doppler.
d
45
Vascular Supply of the Uteroplacentofetal Unit and Techniques for the Examination
1
— A notch is an early diastolic dip. In the second
half of pregnancy this is evidence for an abnormal pulse wave reflection at the level of the spiral aa., presumably because of a faulty tropho-
3.16,3.17).
blast invasion (
Fig. 3.12 Color display of the course of the uterine a. by Doppler spectrum. Normal examination. Note that the uterine a. is
usually located under the skin close to the transducer.
Figs.
— Altered Doppler parameters are less important
in predicting pregnancy risks than the demonstration of notching, which in 70% of cases is
considered to be the determining sign of
developing preeclampsia or of a pregnancy-induced hypertension (PIH).
Fig. 3.13 Normal display of a uterine a.
46
Fig. 3.14 Color display of the uterine a. Normal Doppler examination.
Fig. 3.16 Uterine a. with notch. Fig. 3.17 Color display of the course of the uterine a. and of an
Fig. 3.15 Transvaginal display of the uterine a. by color Doppler and gray-scale Doppler with notch. This can be normal early
in pregnancy.
abnormal flow profile with notch.
왘 Treatments: When abnormalities are found, a trial
of medication to reduce the risks for the pregnancy
has been carried out, for example, administering
low-dose acetylsalicylic acid (ASA). However,
whether these procedures have prevented uteroplacental insufficiency remains to be established.
Examining the Uterine Arteries in the Third
Trimester:
The display of maternal vessels in the third trimester
seems to us to be of little significance, since by that
time pathological changes that could be displayed are
likely to be clinically obvious, for example, preeclampsia or uteroplacental insufficiency with fetal growth
retardation. With elevated maternal blood pressure,
notching of the uterine aa. is to be expected and does
not need to be demonstrated again to ensure the diagnosis.
Displaying the Peripheral Fetal Vessels
The initial diagnostic studies of the peripheral vessels
such as the umbilical a. and the aorta are of crucial significance for further diagnosis. The central vessels are
only examined if the peripheral vessels show abnormal findings. Diagnostic evaluation of the fetal vessels
only becomes important in the third trimester, since
any abnormalities at that stage would lead to a clinical
assessment concerning the need for further obstetric
procedures.
Methods of Examining Specific Vessels
Fig. 3.18 Color display of the three umbilical vessels.
Basic Concepts
Examining the Umbilical Artery:
왘 Examination procedure: For uniform and com-
parable results the umbilical a. should be examined
at its attachment to the placenta. As a rule the origin
of the umbilical a. from the placenta can be displayed without any problems when the placenta is
implanted anteriorly, while examining it when it is
implanted posteriorly is more difficult. Here it may
be impossible to examine the umbilical a. where it
is inserted, and it must be looked for instead in its
narrower parts. It is important to note that the
umbilical cord normally contains three vessels, i. e.,
3.18). An attempt
one vein and two arteries (
may be made to examine the second artery if one
artery is found to be abnormal. Make sure to use an
acute angle.
왘 Flow profile: A moderately steep systolic rise is
succeeded by a relatively elevated diastole.
Sawtooth type display of the Doppler profile
Fig. 3.19).
(
Caution: Because the vessel is tortuous, an exact
value for the angle between the Doppler beam and
the vessels can usually not be ascertained. This error
may lead to a falsely low diastole being displayed.
Fig.
Fig. 3.19 Color display of the umbilical a. by color Doppler and
spectral Doppler. Normal examination.
왘 Normal findings:
— Systolic blood flow may be demonstrated in the
umbilical a. beginning at the 8th week of gestation. Diastolic blood flow may be demonstrated
from the 15th week of gestation.
— The resistance parameters show a slight physio-
logical decline between the 20th and 40th week.
This leads to a slight rise in diastole.
왘 Reference value: An RI below 70 % is normal
(Fig. 3.20a).
왘 Abnormal findings:
— Demonstration of reduced or absent flow (zero
flow) demonstrates pathology, being evidence of
increased resistance with an increasing RI. This
can indicate that the fetus is in danger
Fig. 3.20b).
(
— Flow reversal (reverse flow) during diastole can
rarely be demonstrated and is an extreme variant.
47
Vascular Supply of the Uteroplacentofetal Unit and Techniques for the Examination
1
m/s
0.5
0.3
TAVRI
0.1
20 25 30 35 40
m/s
0.5
0.3
TAM
0.1
20 25 30 35 40
%
100
80
60
40
20
Umbilical a.
20 25 30 35 40
Fig. 3.20 a Time average velocity (TAV), time average maximum velocity (TAM), and resistance index (RI) of the umbilical
a. Mean values and standard deviation of 20 readings for each
week of pregnancy.
Weeks of gestation
Weeks of gestation
Weeks of gestation
왘 Advantages of the examination: Easy to locate and
perform.
왘 Disadvantages of the examination: The angle be-
tween the Doppler beam and the vessel cannot be
determined accurately. This can lead to a false abnormal value of the Doppler parameters, leading to
a falsely low diastolic reading.
In multiple pregnancies there may be difficulties in assigning vessels to the respective child.
왘 Procedure when the findings are ambiguous: Either
take multiple readings or take readings from the
fetal aorta. If it is difficult to assign vessels in multiple pregnancies, take readings from the aortas.
Examining the Aorta in the Second and Third
Trimesters:
왘 Examination procedure: Examine the aorta as far
caudally as possible. Initially display it in cross section at the level of the kidneys. Next, the transducer
is moved back and forth to try and display the aorta
on the left side of the spinal column. The transducer
is now turned to display the aorta longitudinally,
and then it is moved toward the head of the child
and tilted toward the coccyx. This maneuver allows
the aorta to be examined at an acute angle
ig.
F
3.21).
(
왘 Localization: The reading should be taken as far
caudally as possible, close to the bifurcation, since
here an acute angle (less than 60°) between Doppler
beam and vessel can be set. Here the end-diastole is
sufficiently elevated so that it can be distinguished
from an abnormally low value (Figs. 3.22,3.23a, b).
왘 Flow profile: The display should show a peaked sys-
tole and a shallowly domed diastole.
48
Fig. 3.20 b Display of umbilical a. by spectral Doppler. End-di-
astolic zero flow. Abnormal finding.
The prominently elevated systole is distinct from the
low early diastole.
왘 Normal findings:
— Normally systole can be displayed in the 15th
week of gestation, diastole in the 20th week.
— The resistance parameters in the fetal aorta are
higher physiologically at the beginning of the
third trimester than at the end. In general the
range of normal values is relatively limited, allowing the determination of a constant limit
Figs. 3.24a, b).
(
왘 Reference value: An RI below 80 % is normal
(Fig. 3.25).
왘 Abnormal findings:
— With threatening fetal risk diastole will be re-
duced and may disappear (end-diastolic block,
Fig. 3.26). Reversal of diastolic flow just before
delivery is normal.
Fig. 3.21 Schematic diagram
showing the examination of the
fetal aorta. The aorta is first
found as a cross-sectional
image at the level of the kidneys and interrogated avoiding
the vertebral column. The transducer is then turned along the
aorta to display it longitudinally.
To achieve an optimal Doppler
angle for the examination of the
aorta distal to the origins of the
renal arteries, the transducer is
moved toward the infant’s head
and tilted toward the infant’s
coccyx.
왘 Risk estimate using the RI in the aorta:
RI 쏝80 %: Not significant
RI 81−85%: Borderline finding
RI 86−95 %: Abnormal finding
RI 96−100%: Highly abnormal finding
왘 Advantages of examining the fetal aorta: The re-
sistance of the placental vascular bed can be ex-
amined, since the origin of the umbilical a. is immediately adjacent.
Conclusions can be drawn regarding the condition
of the fetal peripheral bed as well as the fetal re-
sponse to pathological changes.
The vessel can be examined without any problems
in multiple pregnancies.
Methods of Examining Specific Vessels
Basic Concepts
Fig. 3.22 Display of the aortic arch and the waveform at the
aortic arch. This is not the place to examine the aorta to determine the condition of the fetus.
Fig. 3.23 a Color Doppler ultrasound display of the aorta with
bifurcation into the iliac aa.
49
Fig. 3.23 b Display of the aorta with forward flow and the inferior vena cava with reverse flow.
Vascular Supply of the Uteroplacentofetal Unit and Techniques for the Examination
m/s
0.5
0.3
TAVRI
1
Fig. 3.24 a Aorta displayed at the bifurcation. The Doppler
spectrum examination is normal.
Fig. 3.24 b Aorta displayed by Doppler spectrum, with display
of reverse flow in the inferior vena cava. 22nd week of gestation.
0.1
20 25 30 35 40
m/s
0.5
0.3
TAM
0.1
20 25 30 35 40
%
100
80
60
40
20
Abdominal fetal aorta
20 25 30 35 40
Fig. 3.25 Time average velocity (TAV), time average maximum velocity (TAM), and resistance index (RI) of the abdominal
fetal aorta. Mean values and standard deviation of 20 readings
for each week of pregnancy.
Weeks of gestationWeeks of gestation
Weeks of gestation
50
Fig. 3.26 Display of aorta with diastolic reverse flow, seen in
the Doppler spectrum in the upper part of the image. Highly abnormal finding.
Examining the Central Fetal Vessels
The middle cerebral a. (MCA) is the most important
central fetal vessel. Unless the fetal periphery displays
pathological changes, the examination of the MCA and
carotid aa. is of little value. It should be noted that fetal
activity can also lower the resistance indices.
Examining the MCA:
왘 Localization: Easy to display bilaterally near the
thalamus.
왘 Examination procedure: The optimal angle for the
examination is obtained by displaying a cross section of the fetal head as for measuring the biparietal
diameter, and aiming vertically at the cerebral falx,
which runs above the MCA. The MCA then runs
toward the transducer on the sphenoid bone at the
3.27).
base of the skull (
Fig.
왘 Flow profile: A peaked systole is clearly distinct
from a low diastole.
As opposed to the carotid a,. diastole is almost always identifiable.
왘 Normal findings:
— Up to about the 30th week of gestation this ves-
sels does not show a diastole, i. e., physiologically
there is zero flow in this vessel. From the 30th
week on there is increasing evidence of a small
diastole, about one quarter the height of systole
ig.
F
3.28).
(
— The height of diastole can vary considerably and
depends on many factors, for example, fetal
movements, the oxygen content of the blood,
amino acids, etc. When Doppler values in the
fetal periphery are abnormal, the mother usually
feels few or no fetal movements, so that in such a
situation fetal activity is not a factor that needs
to be considered as a cause of reduced resistance.
왘 Reference value: An RI over 70 % is normal.
왘 Abnormal findings:
— Analogous to the circulatory centralization in
shock in the adult, one sign of a fetus at risk is an
increase in resistance in the peripheral fetal vessels with a simultaneous decrease in the resistance in the central vessels (brain-sparing
mechanism,
— A rising diastole is a sign of centralization of the
fetal circulation, if at the same time diastole in
the fetal periphery declines, and therefore the
resistance in the vascular b ed rises.
Fig. 3.29).
Methods of Examining Specific Vessels
Fig. 3.27 Color display of the circle of Willis. The head of the
infant has been interrogated laterally. In this setting the MCA
runs toward the transducer.
Basic Concepts
Examining the Carotid Artery:
왘 Localization: In the sagittal section of the fetal neck
(Fig. 3.30a, b).
왘 Flow profile: Peaked systole. Diastolic flow can only
be demonstrated toward the end of pregnancy (Figs.
3.31,3.32).
왘 Normal findings:
— As for the MCA, though the RI is physiologically
somewhat higher (Fig. 3.33.
왘 Abnormal findings:
— A rising diastole indicates centralization of the
fetal circulation.
왘 Disadvantages: The carotid a. is more difficult to ex-
amine, since it is difficult to set the transducer at a
favorable angle. In contrast to the MCA, the carotid
a. is a vessel that is not subject to control. The MCA
therefore seems to show abnormal changes more
readily.
Fig. 3.28 MCA displayed by color Doppler and Doppler spectrum. There is a physiologically low end-diastole.
Fig. 3.29 Doppler ultrasound display of an MCA with very high
diastolic flow. In the presence of a concurrent abnormal finding
in the peripheral fetal vessels or the umbilical a. this may indicate a compensatory shunt in the fetus.
51
Vascular Supply of the Uteroplacentofetal Unit and Techniques for the Examination
Fig. 3.30 b Display of the carotid bifurcation.
1
Fig. 3.31 Display of the carotid a. by color Doppler and Doppler spectrum. Similarly to the MCA, the low end-diastole is normal.
컅 Fig. 3.30 a The carotid a. and jugular v. displayed by color
Doppler
m/s
0.5
0.3
TAVRI
0.1
20 25 30 35 40
m/s
0.5
0.3
TAM
0.1
20 25 30 35 40
Weeks of gestation
Weeks of gestationWeeks of gestation
52
Fig. 3.32 Gray-scale Doppler image of the carotid a. with physiologically low end-diastole.
%
100
80
60
40
20
Fetal common carotid a.
20 25 30 35 40
Fig. 3.33 Time average velocity (TAV), time average maximum velocity (TAM), and resistance index (RI) of the fetal common carotid a. Mean values and standard deviation of 20 read-
ings for each week of pregnancy.
4 Blood Flow Analysis During Pregnancy
This section will describe the physiological and pathological factors influencing blood flow in individual vascular
areas during pregnancy.
Uteroplacental Vessels
The waveforms of the uteroplacental aa. should be examined qualitatively, since quantitative determination
of the blood supply to the uterus and the intervillous
Fig.
space is difficult (
sels are close by, vessels must be localized selectively.
Not only can the Doppler window be placed in the
wrong vessel, but the Doppler sonograms of different
vessels may be superimposed on each other.This is not
always easy to spot (Fig. 4.2). Two criteria must be
evaluated:
1. Indices of the systolic/diastolic velocity changes,
which are a measure of the impedance in the
downstream vascular beds, and hence an indication
of impaired blood flow into the intervillous space.
2. A postsystolic notch in the waveform, which is an
indication of an incomplete trophoblast invasion
(Fig. 4.3). The notch shows the persistence of pulse
wave reflections when the spiral aa. do not dilate,
i.e., are incompletely fetalized.
4.1). Because other maternal ves-
Fig. 4.1 Doppler sonogram of the uterine a.
Basic Concepts
notch.
Fig. 4.2 Doppler sonogram of uterine a. superimposed on the
iliac a.
53
컄Fig. 4.3 Doppler sonogram of uterine a. with postsystolic