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Use of Color Doppler in Echocardiography
Fig. 23.3 Holosystolic tricuspid regurgitation (encoded in yellow)
following drug-induced conversion of fetal supraventricular tachycardia to a sinus rhythm of 132 bpm, demonstrated by M-mode Doppler
echocardiography (29 weeks + 1 day). Diastolic inflow from the right
atrium into the right ventricle is encoded in blue.
Isolated mitral valve regurgitation. Mitral regurgitation as an
23
isolated phenomenon is more commonly a result of left
ventricular outflow tract obstruction in which there is an associated hypoxemia-induced disturbance of left ventricular
myocardial and valvular function, whose end stage is endocardial fibroelastosis.
Semiquantification of AV Valve Regurgitation
While the severity of AV valve regurgitation cannot be quantified by Doppler echocardiographic methods, it can be
assessed by semiquantitative grading.
Pressure–time gradient. The maximum velocity measurement
reflects the pressure gradient that exists between the ventricle
and atrium. This gradient is most strongly influenced by the
pressure within the ventricle, which in turn depends on the afterload (outflow tract obstruction and/or arterial hypertension) and on the filling and myocardial function of the affected
ventricle. It also depends on the pressure at the atrial level. The
pressure–time gradient (
∆p/∆t) of the regurgitant jet provides
information on the systolic function of the ventricle, noting
that the pressure rise is slowed when ventricular function is
impaired. If the maximum velocity of the regurgitant jet is
greater than 4 m/s, this indicates the presence of an outflow
tract obstruction and/or arterial hypertension like that occurring in the recipient twin in fetofetal transfusion. Based on the
simplified Bernouli equation (P
grad
=4V
2
), a maximum re-
max
gurgitant jet velocity of 4 m/s reflects an instantaneous pressure difference of 64 mmHg. The systolic blood pressure of the
fetus does not exceed this value, however
8
.
Spatial extent of the jet. A semiquantitative assessment of the
severity of tricuspid and mitral valve regurgitation is based on
the temporal duration of the regurgitation and on the spatial
extent of the color-flow jet, but the spatial extent of a jet depends more on the velocity of the regurgitated blood than on
its volume. Also, the necessary standardization of instrument
settings and of the Doppler signal display limits the value of
spatial jet parameters in the color Doppler image for the semiquantitative assessment of AV valve incompetence.
Duration of valve regurgitation. For the present, the best pa-
rameter appears to be the temporal duration of AV valve regurgitation, which can be determined by pulsed or CW Doppler or accurately measured in the M-mode color Doppler dis-
12
play
. As a rule, milder degrees of AV valveregurgitation occur
in early to mid-systole while severe, significant regurgitation is
holosystolic. This has been demonstrated in AV canal malformations, where holosystolic AV regurgitation was associated
with the development of fetal hydrops while regurgitation
confined to early and mid-systole did not lead to hydrops
15
Similar studies in fetuses with tachycardia-induced “cardiomyopathies” allow us to assess the severity of myocardial dysfunction: a steady decline in the temporal and spatial parameters for the semiquantification of AV valve incompetence with
increasing time from conversion to sinus rhythm indicates a
steady improvement in myocardial function. The severity of AV
valve incompetence also correlates with the extent of changes
in venous blood flow patterns and with the time required for
the complete remission of hydrops
16, 25
.
.
222
Anomalies of Visceroatrial Blood Flow
Anomalies involving the afferent veins of the heart can be investigated much more easily by the adjunctive use of color
Doppler than by two-dimensional echocardiography alone.
The smaller the fetus, the more difficult it is to differentiate the
pulmonary veins and the veins about the liver, including the
ductus venosus and inferior vena cava, in the gray-scale image
and to define their sites of entry into the corresponding atrium.
These structures are much easier toidentify with color Doppler
sonography, especially when anomalies are present.
Inferior and superior vena cava. For example, when the upper
portion of the inferior vena cava is interrupted, the azygos vein
drains much of the venous blood from the lower half of the
body. In these cases the azygos vein, which generally opens
into the superior vena cava, can be demonstrated more easily
with color Doppler (Fig. 23.
4). This finding is usually seen in
conjunction with a visceral situs ambiguus, especially leftsided isomerism. The same applies to anomalies involving the
umbilical vein and ductus venosus. Color Doppler imaging also
facilitates the diagnosis of a persistent left superior vena cava
by demonstrating blood flow toward the heart.
Anomalous pulmonary venous return. Color Doppler is particularly useful in diagnosing the various types of anomalous pulmonary venous return. These veins are not visible in the grayscale image until the second trimester, but they can be iden-
Anomalies of Atrioventricular Blood Flow
Anomalies of Atrioventricular Blood Flow
tified as early as the 12th week in the color Doppler image. All
types of anomalous pulmonary venous return (supracardiac,
cardiac, and infracardiac) can be diagnosed more easily and
confidently with the aid of color Doppler.
컅 Fig. 23.4 Color Doppler image of blood draining from an azygos vein
into the superior vena cava (30 weeks + 2 days).
Tricuspid and mitral valve atresia. Atresia of the tricuspid and
mitral valve apparatus is easily diagnosed in the two-dimensional image. Color Doppler can additionally demonstrate an
absence of blood flow across the atretic valves. As an aid to
differential diagnosis in fetuses with outflow tract obstructions in the right and left heart, the pulse repetition frequency
should be progressively lowered during the examination, since
there may still be low-velocity inflow into the hypoplastic right
or left ventricle in fetuses with pulmonary atresia and a hypoplastic right heart or in fetuses with aortic atresia and a hypoplastic left heart (Fig. 23.
across the foramen ovale is typically present in these cases of
severe left ventricular obstruction and is much easier to visualize with color Doppler sonography.
Fig. 23.5 Hypoplastic lef t heart with endocardial fibroelastosis resulting from a severe aortic obstruction (21 weeks). Flow across the
mitral valve into the left ventricle (lv) can be demonstrated only when
a very low pulse repetition frequency is used.
5). An interatrial left-to-right shunt
Tricuspid valve dysplasia and Ebstein’s anomaly. Both in tri-
cuspid valve dysplasia and in Ebstein’s anomaly of the tricuspid
valve, severe tricuspid regurgitation can develop during fetal
life, leading to massive enlargement of the right atrium. Less
commonly there may be venous pressure elevation sufficient
to cause fetal hydrops. Here again, color Doppler can aid in the
diagnosis and semiquantitative grading of tricuspid valve re-
gurgitation. Color Doppler M-mode echocardiography can be
used to measure the duration of the regurgitant jet, and twodimensional color Doppler echocardiography can be used to
determine the length and area of the jet as described above.
Associated outflow tract obstruction. Tricuspid regurgitation
is especially pronounced in cases of associated outflow tract
obstruction (pulmonary atresia, pulmonary stenosis), with
some authors placing tricuspid dysplasia with pulmonary
valve atresia under the heading of pulmonary atresia with an
intact interventricular septum. However, unlike pulmonary
atresia with an intact interventricular septum and without tricuspid dysplasia, hypoplasia of the right ventricle does not
occur in pulmonary obstructions with tricuspid dysplasia
(Fig. 23.
these cases. It should be noted that even when the pulmonary
valve is patent in cases of pronounced tricuspid valve dysplasia
with severe tricuspid regurgitation, there will no longer be any
detectable forward flow across the pulmonary valve
these cases the entire pulmonary arterial bed is perfused by
retrograde flow through the ductus arteriosus, mimicking the
classic features of pulmonary valve atresia in the antenatal period. Once the infant has been delivered, forward flow occurs
across the pulmonary valve because the right ventricular afterload becomes substantial due to the fall in pulmonary vascular
resistance.
2). The right ventricle may even be dilated in some of
5, 33
.In
Specific Obstetric Problems
223
Use of Color Doppler in Echocardiography
Anomalies of Ventriculoarterial Blood Flow
Pulmonary and aortic stenosis. Stenoses of the pulmonary
valve and aortic valve generally produce a turbulent color-flow
pattern behind the valve, accompanied by prestenotic flow acceleration in front of the valve (Fig. 23.
ventricular septal defect is present, however, even a very highgrade stenosis may not produce a turbulent pattern because
the blood is easily routed through the ventricular septal defect
into the other major artery (e.g., into the overriding aorta with
pulmonary stenosis). In these cases, retrograde blood flow can
be detected in the artery with the stenotic valve, i.e., reverse
perfusion of the pulmonary arterial bed through the ductus
arteriosus in cases of severe pulmonary stenosis, and reverse
flow from the ductus arteriosus into the aortic arch and ascending aorta in cases of severe aortic stenosis with a ventricular septal defect. These blood flow patterns are characteristicof
atresias of the great arteries and are an important aid to differential diagnosis. The basic rule still applies, however, that abnormal blood flow patterns like those associated with stenotic
jets or reverse blood flow due to severe valvular obstructions
should always be confirmed by pulsed Doppler spectral analy-
23
6). If a relatively large
sis. Even with severe hypoplasia of the aortic arch, an isolated
coarctation of the aorta, or an interruption of the aortic arch
(types I–III), color Doppler flow imaging is very helpful for accurately defining the anatomical relationships.
Hypoplasia of the associated arteries. When a severe valve ob-
struction (stenosis or atresia) is present, the associated artery
is usually hypoplastic. With two-dimensional echocardiography, it is often extremelydifficult to define the hypoplasticvessel and thus differentiate between aortic atresia, pulmonary
atresia, and a common truncus arteriosus. Color Doppler echocardiographycan be very helpful in these cases by demonstrating reverse blood flow in the hypoplastic artery (Fig. 23.
with a common truncus arteriosus, by showing the pulmonary
arteries arising from a common trunk. The same is true in a
double-outlet right ventricle with or without pulmonary stenosis, which often coexists with a malposition of the great vessels (Fig. 23.
anomalies, a turbulent blood flow pattern is not necessarily
found in the pulmonary artery even with severe pulmonary
stenosis, because blood can easily drain from the right ventricle into the overriding aorta as a result of intrauterine circulatory dynamics. For this reason, the magnitude of the pressure
gradient cannot be appreciated until postnatal circulatory
adaptation is completed.
8), and in the tetralogy of Fallot. In either of these
7 )or,
Transposition of the great vessels. Transposition of the great
vessels, which more often takes the form of an “uncorrected”
D-transposition than a “corrected” L-transposition, is also accessible to diagnosis by two-dimensional echocardiography.
Again, however, color Doppler echocardiography makes it eas-
a
224
b
Fig. 23.6 Critical aortic stenosis (20 weeks + 5 days).
a Normal-appearing four-chamber view in two-dimensional echocar-
diography.
b With color Doppler echocardiography, the aortic stenosis can be diagnosed by the stenotic jet in the initial segment of the ascending
aorta.
Fig. 23.7 Hypoplastic left heart with aortic atresia (31 weeks). The
aortic arch (aa) and hypoplastic ascending aorta (aao, diameter
2.5 mm) are perfused entirely by retrograde blood flow from the ductus ar teriosus. The descending aorta (dao) is perfused by antegrade
flow.
Anomalies of Blood Flow through the Cardiac Septa
Fig. 23.8 Double-outlet right ventricle (DORV) with malposition of
the great arteries. Blood ejected from the left ventricle passes through
a VSD into the aorta, which arises entirely from the right ventricle. The
pulmonary artery is hypoplastic but can be identified as a second vessel, also carrying antegrade flow, that runs parallel to the aor ta.
ier to locate the abnormally positioned arteries, especially in
cases with associated pulmonary stenosis and in early echocardiography. As in other anomalies, color Doppler echocar-
Fig. 23.9 D-transposition of the great arteries with a VSD (32 weeks
+ 2 days). The origin and parallel course of the two great arteries can
be appreciated. The color Doppler image also shows a systolic left-toright shunt through a small outlet VSD.
by detecting or excluding associated malformations of the
heart with greater certainty than two-dimensional echocardiography alone (Fig. 23.
diography can increase the accuracy of fetal echocardiography
Anomalies of Blood Flow through the Cardiac Septa
Interatrial shunt reversal. Color Doppler flow mapping can
clearly demonstrate the physiological right-to-left interatrial
shunt, both in the four-chamber view and in the basal shortaxis view at the level of the origin of the great arteries (“circle
and sausage view”). The latter view shows that the blood flow
from the ductus venosus is directed across the foramen ovale
into the left atrium, while blood from the inferior vena cava
passes through the tricuspid valve into the right ventricle. A re-
versal of the interatrial shunt, with shunting of blood from the
left atrium to the right atrium, occurs when the pressure in the
left atrium is elevated due, for example, to a severe outflow
tract obstruction at the aortic level.
Atrioventricular septal defect. Atrioventricular septal defect
(synonyms: AV canal defect, endocardial cushion defect) is a
combined defect involving the atrial septum primum and the
ventricular septum in the inflow tract. Usually it is associated
with a malformation of the AV valve apparatus. This anomaly is
easily diagnosed with two-dimensional echocardiography.
Color Doppler sonography confirms the diagnosis by demonstrating common blood flow into both ventricles and also
showing AV valve regurgitation, which is almost always present in this defect. With very severe AV valve regurgitation in
the setting of an atrioventricular septal defect, the rising pressure in the right atrium may lead to venous pressure elevation
and fetal hydrops
15
. The semiquantitative evaluation of AV
valve regurgitation in fetuses with atrioventricular septal defect was describ ed earlier in the section on valve regurgitation.
Ventricular septal defects. Most isolated ventricular septal defects are perimembranous defects that involve the pars membranacea of the interventricular septum and an adjacent part
of the muscular septum. Most of these defects are large and are
easily appreciated in the two-dimensional echocardiogram.
Muscular ventricular septal defects in the outflow tract, which
qualify as a form of conotruncal anomaly, are usually so large
that they can be diagnosed in the two-dimensional echocardiogram. They are frequently combined with an overriding
aorta, often as part of a tetralogyof Fallot or double-outlet right
ventricle.
Bidirectional shunt across a ventricular septal defect. The most
common ventricular septal defects are small defects located in
the trabecular part of the muscular septum. They are extremely difficult to diagnose prenatally, and most are not detectable in the two-dimensional image. Color Doppler echocardiography is the only technique available for diagnosing
these defects. As noted earlier, it is essential that variance mapping be used. Because pressure differences between the right
and left ventricles are either absent or very small due to the
parallel arrangement of the fetal circulatory system, transient
pressure differences arise during the cardiac cycle and increase
during late pregnancy. As a result, color Doppler can demonstrate turbulent shunts across the interventricular septum,
with maximum blood flow velocities of approximately 40 cm/s
in the second trimester and 1.20 m/s at term
right-to-left shunt is observed in systole and a left-to-right
9).
13
. Typically, a
Specific Obstetric Problems
225
Use of Color Doppler in Echocardiography
a b
226
Fig. 23.10 Small, muscular ventricular septal defect with a bidirec-
tional shunt pattern, not appreciated in the two-dimensional image
(25 weeks + 3 days).
shunt in diastole (Fig. 23.10). This observation may be due to
differences in the patterns of excitation and relaxation and
23
changes in the afterload of both ventricles (the afterload of the
right ventricle is nearly constant in the second and third
trimesters, while the afterload of the left ventricle rises
steadily until term). The effect of afterload on shunt direction is
supported by the observation that, with a D-transposition of
the great arteries, a left-to-right shunt occurs across the
ventricular septal defect in systole (Fig. 23.
left shunt occurs in diastole
13
.
9) while a right-to-
Color Doppler Sonography in Fetal Arrhythmias
Tachycardia-induced “cardiomyopathy.” Color Doppler sono-
graphy is necessary in the diagnosis and classification of fetal
arrhythmias only when done as part of a complete echocardiographic workup of the fetus to exclude associated cardiac
anomalies. Also, functional disturbances that are secondary to
fetal arrhythmias are manifested in the form of AV valve regurgitation, which can be diagnosed and semiquantitatively
analyzed with color Doppler, as described above. AV valve regurgitation in the setting of fetal arrhythmias most commonly
occurs in association with tachyarrhythmias (tachycardia-induced “cardiomyopathy”) and complete AV block. In the latter
condition, pulmonary valve insufficiency has been observed in
the setting of cardiac decompensation.
Differential diagnosis of fetal arrhythmia. The diagnosis and
differential diagnosis of fetal arrhythmias are based on the
demonstration of wall motion, valve motion, and blood flow
patterns with a high temporal resolution. This is best accomplished by the use of M-mode echocardiography and pulsed
Doppler echocardiography
blood flow patterns in different segments of the heart are recorded and analyzed for their temporal relationships. By dem-
18
. Wall and valve movements and
a A right-to-left shunt is present during systole.
b A left-to-right shunt appears during diastole.
Unidirectional shunts across a ventricular septal defect. If the
shunt across a ventricular septal defect is in one direction only,
the presence of an inflow tract obstruction and/or an outflow
tract obstruction should be excluded. For example, tricuspid
valve atresia is associated with the presence of a unidirectional
left-to-right shunt across the ventricular septal defect. Other
unidirectional shunt patterns consist of a right-to-left shunt
due to pulmonary stenosis with a ventricular septal defect or a
left-to-right shunt due to aortic stenosis and atresia with a
ventricular septal defect.
onstrating the effects of electrical excitation in the heart (atrial
and ventricular systoles, opening movements of the AV and
semilunar valves, ventricular inflow and outflow), the examiner can obtain indirect information on the spread of the
cardiac impulse and diagnose the type of arrhythmia that is
present
18
.
Color Doppler M-mode echocardiography. The same M-mode
beam can be used to simultaneously record a conventional Mmode echocardiogram and a color-flow map, with correspondingly high temporal resolution. With proper placement of the
M-mode beam, a precise analysis can be made of the time intervals between hemodynamic events in veins, atria, ventricles, and arteries. The movements of the cardiac valves and
walls are simultaneously recorded so that they can be correlated with hemodynamic events and the latter can be correlated with specific phases of the cardiac cycle. With color Mmode echocardiography, then, it is almost always possible to
classify the underlying arrhythmia. This cannot always be done
with conventional M-mode echocardiography, whether because of an unfavorable fetal lie or insufficient wall motion
during atrial contractions
12
.
Summary
Summary
Information added by color Doppler sonography of the fetal
heart. Color Doppler mapping of blood flow patterns in the
fetal heart and in the veins and arteries leading to and from the
heart is an essential part of the echocardiographic examination
of the fetus
32
. While most heart defects can be diagnosed by
means of two-dimensional structural analysis, the addition of
color Doppler imaging supplies a variety of additional, essential information (Tables 23.
1, 23.2). Some heart defects can be
detected only with the aid of color Doppler echocardiography.
For others, the rapid screening of the fetal heart for flow abnormalities yields important information that, when combined
with subsequent pulsed or CW Doppler spectral analysis,
makes it possible to diagnose valvular stenosis, valvular insufficiency, and interventricular shunts. In cases with complex
heart defects, color Doppler sonography is an essential tool for
making a confident diagnosis that encompasses all cardiac abnormalities. With some defects, moreover, color Doppler supplies additional parameters that provide more individualized
information on prognosis and on the further intrauterine and
postnatal course of the disease.
Role of fetal color Doppler echocardiography. Various authors
have attempted to define the role of color Doppler echocardiography within the framework of fetal echocardiography. For
example, Copel et al.
7
found in their retrospective analysis of
fetal cardiac abnormalities that Doppler color-flow mapping
was essential to the correct anatomical diagnosis in 29% of the
fetuses, was helpful but not essential in 47%, was not helpful in
24%, and even led to misinterpretations in several cases. Froma
critical standpoint, however,it should be noted that this type of
study depends strongly on the experience of the examiner. It
also depends on the technique that is used in conducting the
examination (one examiner makes heavy use of color Doppler
in locating cardiac structures, another examiner less so) and
also on the technical quality of the two-dimensional image and
the color Doppler echocardiogram. Another key factor is gestational age. Cardiac structures are generally easier to define in
Table 23.1 General advantages of color Doppler sonography
➤
Rapid screening of the heart for abnormal flow patterns
(variance mapping) to detect or exclude jets associated with
stenosis, valve regurgitation, or interventricular shunts.
➤
Rapid and optimum placement of the Doppler sample volume
for absolute flow measurements and the qualitative evaluation
of blood flow patterns.
➤
More rapid localization of normal cardiac structures, especially
in early examinations for heart defects.
➤
Particularly advantageous in identifying hypoplastic arteries
and demonstrating retrograde blood flow patterns in those
vessels (diagnosis and differential diagnosis of severe pulmonary stenosis, pulmonary atresia, severe aortic stenosis, aortic
atresia, and common truncus arteriosus).
➤
In selected cases, the intrauterine blood flow patterns make it
possible to determine the severity of the heart defect and offer
an intrauterine and postnatal prognosis.
Table 23.2 Relevant diagnostic information that color Doppler echocardiography adds to two-dimensional echocardiography for various
heart defects
Heart defect Information added by color Doppler
sonography
Interrupted
inferior vena
cava
Anomalous
pulmonary
venous return
Type I atrial
septal defect
Complete
atrioventricular
septal defect
Tricuspid
dysplasia,
Ebstein anomaly
Tricuspid atresia No evidence of antegrade flow through the
Pulmonary
atresia with an
intact IVS
Pulmonary
atresia with a
VSD
Pulmonary
stenosis without
aVSD
Pulmonary
stenosis with a
VSD (also
combined with
other heart
defects)
Aortic atresia
with a
hypoplastic left
heart
Aortic stenosis Stenotic jet at the aortic valve; a critical aortic
Demonstrates caudocranial blood flow in the
azygos vein parallel to the descending aorta
and its junction with the superior vena cava
Locates the pulmonary veins and demonstrates
their anomalous termination at the supra-,
intra- or infracardiac level
Associated mitral valve regurgitation
Inflow into both ventricles through a common
AV valve; demonstration and semiquantitation
of AV valve regurgitation, including multiple
jets
Demonstration and semiquantitation of
tricuspid valve incompetence; evaluation of
right ventricular outflow tract and pulmonary
valve (caution: pulmonary artery flow may be
retrograde even with an open pulmonary valve)
tricuspid valve; rudimentary right ventricle is
filled through a VSD; helpful in evaluating the
position of the great arteries
Shows only retrograde perfusion of the
pulmonary arteries via the ductus arteriosus;
demonstrates inflow through the dysplastic
tricuspid valve into the hypoplastic right
ventricle, also tricuspid valve regurgitation
Demonstrates only retrograde flow through the
ductus arteriosus into the generally hypoplastic
pulmonary arterial system; blood flow from the
right ventricle into the broad aorta, which is
usually overriding
Shows a stenotic jet at the pulmonary valve
May not demonstrate a stenotic jet when a
large VSD is present; may show additional or
exclusive retrograde blood flow in the
pulmonary arterial system via the ductus
arteriosus
Shows only retrograde blood flow in the aortic
arch and ascending aorta; no inflow (mitral
atresia) or scant inflow (mitral valve dysplasia)
into the hypoplastic left ventricle and mitral
insufficiency; left-to-right shunt across the
foramen ovale
stenosis with initial left ventricular dysfunction
is marked by mitral valve regurgitation and
increasing retrograde flow through the aortic
arch, accompanied by an interatrial left-to-right
shunt
Continued 컄
Specific Obstetric Problems
227
Use of Color Doppler in Echocardiography
228
Table 23.2 (Continued)
Heart defect Information added by color Doppler
sonography
Coarctation of
the aorta,
tubular
hypoplasia of
the aortic arch,
interrupted
aortic arch
Double-outlet
right ventricle
Locates and defines the hypoplastic arch
segment and origins of the brachiocephalic
arteries; differentiates coarctation from
interrupted aortic arch; classifies the
interrupted arch as to type; demonstrates
blood flow through an associated ventricular
septal defect
Defines the usually underdeveloped pulmonary
artery; may show accelerated or disturbed flow
patterns in the pulmonary valve area due to
pulmonary stenosis
Tetralogy of
Fallot
Defines the usually underdeveloped pulmonary
artery; may show accelerated or disturbed flow
patterns in the pulmonary valve area due to
pulmonary stenosis
Absentpulmonary
valve syndrome
Demonstrates bidirectional flow in the dilated
pulmonary arteries with stenotic and/or
regurgitant patterns in the area of the absent
pulmonary valve; detects or excludes
23
Transposition of
the great
arteries
associated agenesis of the ductus arteriosus
Confirms the two-dimensional
echocardiographic diagnosis and demonstrates
small ventricular septal defects; with a
“corrected” transposition, occasionally shows
accelerated or disturbed flow patterns in the
pulmonary valve area due to associated
pulmonary stenosis
Ventricular
septal defect
(VSD)
Small muscular VSDs can be diagnosed only by
the interventricular jet revealed by color
Doppler echocardiography; typical bidirectional
shunt pattern with systolic right-to-left shunt
and diastolic left-to-right shunt through the
VSD; unidirectional shunts signify additional
obstructions in the inflow tract and/or outflow
tract; with transposition of the great arteries,
the biphasic shunt pattern is reversed
the B-mode image in late pregnancy than in early pregnancy.
For examinations performed in the late first trimester and
early second trimester, color Doppler echocardiography is of
crucial importance not only in diagnosing cardiac anomalies
but also in locating and identifying normal blood vessels
Specific heart defects. There are a number of heart defects for
which color Doppler echocardiography provides essential additional information (Table 23.
2). Color Doppler is the only
technique that can detect small muscular ventricular septal
defects, which are associated with demonstrable intracardiac
shunts starting in the mid-second trimester. Color Doppler also
adds essential information in the diagnosis of anomalies of the
great arteries, especially when one of the arteries is hypoplastic. Color Doppler in these cases aids in localizing the vessels,
which is often difficult in cases of malposition and transposition where one of the arteries is hypoplastic. Semilunar valve
stenosis can also be diagnosed more easily with color Doppler
but requires confirmation by Doppler spectral analysis. Finally,
17, 2 0
color Doppler echocardiography appears to be essential in the
diagnosis of total anomalous pulmonary venous return because these vessels are difficult to define with two-dimensional echocardiography, even in the second trimester.Another
domain of color Doppler echocardiography is in locating sites
of AV valve regurgitation, which can be semiquantitatively analyzed with Doppler echocardiography. Some of these sites are
physiological, but others occur in association with cardiac and
extracardiac fetal anomalies. Color flow can also improve the
accuracy of spectral Doppler measurements and volumetry for
determining ventricular outflow, since preliminary color
Doppler echocardiography can be used to find the most
favorable insonation angle for spectral Doppler echocardiography.
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Specific Obstetric Problems
229
Structure of the Human Placenta and Pathomorphological
24
Changes in Placental Insufficiency
K. R. Reitnauer
Structure of the Human Placenta
Weight and Dimensions
The human placenta is a disk-shaped organ composed of the
fetal chorionic plate, which bounds the amniotic cavity along
with the three-vessel umbilical cord; the basal plate with
the spiral arteries and veins, which bounds the uterine
wall; and the intervening villi with the intervillous spaces
(Fig. 24.
24
the fetal villous trees are immersed in the maternal blood. Because of this arrangement, the fetal chorionic epithelium that
lines the villi is bathed directly by maternal blood
the placenta has an approximate weight of 500 g, a diameter of
17–19cm, a basal surface area of 250 cm
2–2.5 cm.
1).
The human placenta is of the hemochorionic type, in which
15
2
, and a thickness of
.Atterm
Umbilical cord
Villous network
Myometrium Spiral artery Basal plate Septum Vein Anchoring villus
Fig. 24.1 Schematic diagram of the mature human placenta. (Modified from Schiebler and Kaufmann.)
Intervillous space
Chorionic plate
Early Development of the Human Placenta
Five stages (Fig. 24.2a–e) can be recognized in the early
development of the human placenta
Preimplantation stage. The preimplantation stage begins with
formation of the zygote,which matures to a blastocyst through
repeated cell divisions. The blastocyst consists of an inner
embryoblast and outer trophoblast (Fig. 24.
Stage of the implanted blastocyst. At this stage, which begins
on about day 7 after fertilization, the embryonic pole reaches
the endometrium and adheres to it. This is followed by a rapid
increase in the thickness of the trophoblast, which actively
penetrates the endometrium through a histolytic action.
Two types of trophoblastic cell can be distinguished at this
stage: an outer syncytiotrophoblast, so named because it is
formed by the fusion of adjacent cells, and an inner cytotrophoblast, which functions as a stem cell pool for the syncytiotrophoblast.
Increasing numbers of lacunae form within the syncytiotrophoblast, separated from one another by syncytial
trabeculae. By about the 12th day after fertilization, the implanted blastocyst is completely covered by the endometrium
(Fig. 24.
2b).
5, 6, 30, 46
.
2a).
Primary villi. The “primary villi” are now formed by the in-
growth of cytotrophoblastic cells from the primary chorionic
plate into the central portions of the trabeculae (Fig. 24.
Secondary villi. Connective tissue cells migrate from the extraembryonic mesoderm of the chorionic cavity along the axis
of the primar y villi, transforming the latter into secondary villi.
Only the basal portions of the villi are spared and remain in the
primary villus stage; they form the cell columns. The adjacent,
confluent lacunar system becomes the intervillous space. As
the trophoblast burrows deeper into the endometrium, it
erodes maternal blood vessels, causing maternal blood to
bathe the intervillous space (Fig. 24.
Tertiary villus stage. The tertiary villus stage begins on about
day 18 postconception. It is characterized by the formation of
embryonic capillaries and hematopoietic stem cells from the
mesenchymal cells located in the villi. This is accompanied by
an ingrowth of the “allantoic vessels” from the embryo across
the umbilical cord and chorionic plate into the villi. These vessels gain attachment to the capillaries that develop locally in
the villi (Fig. 24.
development of an embryoplacental circulation
2e), creating the necessary foundation for the
2d).
13,30, 34
2c).
.
230
Structure of the Human Placenta
CT
EB
ST
E
D
CT
EB
ST
L
MBV
D
ab
CP
CT
ST
PVL
L
MBV
D
CP
EM
CT
IVLS
SVL
ST
CC
MBV
D
Specific Obstetric Problems
c d
FBV
EM
CT
IVLS
ST
TVL
CC
MBV
D
e
Chorion frondosum. The embryo in the 8th week of gestation is
surrounded, from inside to outside, by the amniotic cavity, the
amnion, and the adjacent chorionic cavity. Outside this are the
chorionic plate, the trabecular and lacunar system described
above, and the basal plate. The latter structures form a uniform,
bushy chorion frondosum (Fig. 24.
3). The outermost structures
are the decidua basalis and decidua capsularis. The decidua
parietalis lines the uterine cavity (Fig. 24.
4a).
Fig. 24.2 Diagrams tracing the early development of the human
placenta. (Modified from Schiebler and Kaufmann.) EB = embryoblast;
CT = cytotrophoblast; ST = syncytiotrophoblast; E = endometrium;
D = decidua; L = lacuna; MBV = maternal blood vessel; CP = chorionic
plate; PVL = primary villus; SVL = secondary villus; TVL = tertiary villus;
IVLS = intervillous space; CC = cell column; EM = extraembryonic mesoderm; FBV = fetal blood vessel.
a Preimplantation stage, up to day 6 postconception.
b Implantation stage, days 7–12 postconception.
c Primary villus stage, days 13–15 postconception.
d Secondary villus stage, days 15–20 postconception.
e Tertiary villus stage, from day 18 postconception.
Chorion laeve. While vascularization of the villi starts at the
implantation pole toward the end of the 3rd week of gestation,
the villi located at the pole facing the uterine lumen begin to
regress. This regression is well advanced by the 10th week,
creating an almost villus-free chorion laeve that can be distin-
guished from the placenta. Starting in about the 14th week, the
embryonic membranes become increasingly apposed to the
uterine wall (Fig. 24.
mentary and partially fuses with the decidua parietalis
4b). The decidua capsularis becomes frag-
5, 6, 15,34
231
.