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COMMON INDICATIONS FOR FETAL
ECHOCARDIOGRAPHY
Abnormal heart on screening ultrasound
Hydrops
Polyhydramnios
Fetal arrhythmia
Chromosomal anomalies
Extracardiac anomalies
Family history (CHD, syndromes associated with
CHD)
Maternal disease (diabetes, collagen vascular,
phenylketonuria)
Teratogen exposure
Increased nuchal translucency on first-trimester
screening
Monitoring response to intrauterine therapy
Monitoring fetus at risk for decompensation
(persistent tachyarrhythmia, hydrops)
CHD, Congenital heart disease.
Cardiac axis and position are normally such that the
apex of the heart points to the left and the bulk of the
heart is in the left chest (Fig. 37-1, A). This is levocardia.
In mesocardia the heart is central with the apex pointing
anteriorly. In dextrocardia the apex is directed rightward, and the heart is primarily in the right chest. This
abnormality must be distinguished from dextroposition
(Fig. 37-1, B), in which the heart maintains a normal
axis but is displaced to the right by an external process,
such as a left chest mass or pleural effusion. Abnormal
cardiac axis is associated with a 50% mortality and
abnormal cardiac position with an 81% mortality.
21
The fetal cardiovascular system contains several unique
shunts: the ductus venosus, foramen ovale, and ductus
arteriosus (Fig. 37-2). Antenatally, the placenta rather
than the lungs is the fetus’ sole source of oxygen. Oxygenated blood leaves the placenta through the umbilical
vein and travels through the ductus venosus and inferior
vena cava to the fetal right atrium. As a result of laminar
flow, much of this blood is shunted across the foramen
ovale to the left atrium and then into the left ventricle,
aorta, and the fetal brain. Poorly oxygenated blood from
the superior vena cava also enters the right atrium but
preferentially enters the right ventricle and pulmonary
artery because of the unique flow pattern. Most of this
blood is shunted through the ductus arteriosus into the
descending aorta. Thus, these shunts function so that the
majority of output from both ventricles enters the systemic circulation, rather than a substantial portion entering the pulmonary circulation, as in the adult. Normal
values for measurements of the fetal heart and great
vessels are shown in Figures 37-3 and 37-4.
Fetal echocardiography is best accomplished between
18 and 22 weeks of gestation.
22
Before 18 weeks,
Chapter 37 ■ The Fetal Heart 1297
A
RA
SP
RV
LA
LV
B
FIGURE 37-1. Heart position. A, Normal position of the
heart. The heart is predominantly in the left chest, with only the
right atrium in the right chest. There is a normal cardiac axis of
(dashed line) of 40 degrees from the midline (solid line). B, Dex-
troposition of fetal heart caused by a large, congenital cystic
adenomatoid malformation. Transverse image through the fetal
chest shows the heart displaced to the right, but the apex remaining leftward. LA, Left atrium; LV, left ventricle; RA, right atrium;
RV, right ventricle; SP, spine.
resolution is frequently limited by the small size of the
fetal heart. After 22 weeks the examination may be compromised by progressive ossification of the fetal skull,
spine, and long bones; the relatively smaller amniotic
fluid volume; and unaccommodating fetal position. In
some cases, first-trimester evaluation of the fetal heart
may be accomplished with endovaginal ultrasound as
early as 11 to 14 weeks.
23-25
However, first-trimester fetal echocardiography is
limited and should be considered an adjunct to secondtrimester evaluation, not a replacement.
Scanning the fetal heart requires a systematic approach,
beginning with determination of the position of the fetus
1298 PART IV ■ Obstetric Sonography
Ductus
arteriosus
Foramen
ovale
Ductus
venosus
Umbilical
vein
Umbilical
arteries
Placenta
FIGURE 37-2. Diagram of fetal circulation. Blood from the umbilical vein is shunted through the ductus venosus to the right
atrium and then across the foramen ovale to the left atrium. Most of the fetal cardiac output is shunted to the descending aorta through
the ductus arteriosus.
within the uterus and the heart within the fetal chest. A
transverse view through the fetal thorax above the level
of the diaphragm demonstrates four cardiac chambers.
Four-chamber views can be obtained with the angle of
insonation parallel to the interventricular septum (apical
four-chamber view; Fig. 37-5, A; Video 37-1 ) or per-
pendicular to the septum (subcostal four-chamber view;
Fig. 37-5, B; Video 37-2). In a four-chamber view the
echogenic foraminal flap of the foramen ovale can be
observed moving into the left atrium at twice the heart
rate. With slight angulation, the superior pulmonary
veins may be seen entering the spherical left atrium (Fig.
37-5, C). The atrioventricular valves are visible in the
four-chamber view. The septal leaflet of the tricuspid
valve inserts more apically than that of the mitral valve.
The left ventricle has a relatively smooth inner wall. The
internal surface of the right ventricle is coarse, particularly near the apex, where the moderator band of the
trabecula septomarginalis is frequently recognized as a
small, bright, echogenic focus. This helps identify the
morphologic right ventricle.
From the subcostal four-chamber view, angling the
transducer towards the fetus’ right shoulder permits
evaluation of the continuity of the left ventricle with the
ascending aorta (Fig. 37-6). Further angulation in the
same direction shows the right ventricle in continuity
with the pulmonary artery (Fig. 37-7; Videos 37-3
and 37-4). The diameter of the pulmonary artery is
approximately 9% larger than that of the aorta between
14 and 42 weeks. The measured differences in these
vessels and with M-mode versus two-dimensional (2-D)
imaging are negligible (2%-5%) for both the pulmonary
artery and the aorta.
26
Further rightward rotation produces a sagittal view of the fetal thorax and a short-axis
view of the ventricles (Fig. 37-8; Video 37-5). Angulation toward the left fetal shoulder from this view shows
the aorta as a central circle, with the pulmonary artery
draping anteriorly and to the left (Fig. 37-9).
The apical four-chamber view may also be used as a
starting point when evaluating normal cardiac anatomy.
Yagel et al.27 describe a series of planes arising from the
apical four-chamber view, all accomplished by moving
the transducer in a cephalad direction. A slight cephalad
advancement will show an apical five-chamber view,
which is useful in accessing continuity of the ascending
aorta with the left ventricle (Fig. 37-10). Continued
cephalad movement should result in visualization of the
bifurcating pulmonary artery and its relationship to the
right ventricle. A three-vessel and trachea view should
be visualized next (Fig. 37-11; Video 37-6). This view
allows evaluation of the main pulmonary artery–ductus
arteriosus confluence, the transverse aortic arch, and the
superior vena cava. Comparison of vessel size, confirmation of vessel presence, and direction of blood flow with
color Doppler can all be assessed at this level. Additionally, correct location of both great vessels to the left of
Chapter 37 ■ The Fetal Heart 1299
A
C
B
D
E
FIGURE 37-3. Cardiac dimensions. A, Left ventricular internal dimension versus gestational age. y = 0.049x –0.262. B, Right
ventricular internal dimension versus gestational age. y = 0.045x –0.228. C, Posterior left ventricular wall thickness versus gestational age.
y = 0.012x –0.063. D, Septal thickness versus gestational age. y = 0.012x –0.088. E, Left atrial internal dimension versus gestational age.
y = 0.040x –0.214. In each graph, the 95% confidence limits represent twice the standard error of the mean. (From Allan LD, Joseph MC,
Boyd EG, et al. M-mode echocardiography in the developing human fetus. Br Heart J 1982;47:573-583.)
1300 PART IV ■ Obstetric Sonography
A
B
FIGURE 37-4. Diameter of aortic root and pulmonary artery. A, Diameter of aortic root versus gestational age.
B, Diameter of pulmonary artery (PA) versus gestational age. Norms and confidence limits for echocardiographic measurements. (From
Cartier MS, Davidoff A, Warneke LA, et al. The normal diameter of the fetal aorta and pulmonary artery: echocardiographic evaluation in
utero. AJR Am J Roentgenol 1987;149:1003-1007.)
27
the trachea can be determined.
Returning to a sagittal
plane of the fetus, directing the transducer from the left
shoulder to the right hemithorax, demonstrates the distinctive candy-cane shape of the aortic arch (Fig. 37-12;
Videos 37-7 and 37-8). The three major vessels to the
head and neck and the ductus arteriosus may be seen.
The aortic arch should not be confused with the ductal
arch (Fig. 37-13), which is formed by the right ventricu-
lar outflow tract, pulmonary artery, and ductus arteriosus. The ductal arch is broader and flatter than the aortic
arch. Lastly, sliding the transducer to the right while
maintaining a sagittal plane on the fetus should allow
visualization of the inferior and superior vena cava entering the right atrium.
M-mode echocardiography provides a 2-D image of
motion over time. It is useful in evaluating heart rate,
chamber size, wall thickness, and wall motion (Fig.
37-14). Simultaneous M-mode imaging through an
atrium and ventricle is helpful in analyzing arrhythmias
(Fig. 37-15). Chamber size and function should be evaluated at the level of the atrioventricular valves.
28
Spectral Doppler ultrasound evaluation of the fetal
heart can be used to determine the velocity of flow
through the vessels or valves (Fig. 37-16) as well as regur-
gitant flow into the chambers of the heart (Fig. 37-17).
Variation in flow velocity may reflect structural or functional cardiac abnormalities. For example, a stenotic
atrioventricular valve will be associated with an abnormal
flow pattern through the affected valve. Spectral Doppler
ultrasound is useful in assessing the functional significance of structural abnormalities and arrhythmias.
Color Doppler ultrasound permits a rapid interrogation of flow patterns within the heart and great vessels
(Fig. 37-18), allowing functional and structural abnormalities to be more rapidly characterized. For example,
valvular stenosis is clearly demonstrated with color
Doppler ultrasound, as is reversed flow through insufficient valves or in the great vessels. Color Doppler ultrasound reduces the amount of time required for Doppler
ultrasound evaluation of the heart, while improving the
accuracy of fetal echocardiography, particularly in the
setting of complex cardiac anomalies.
29-32
Subtle lesions
such as small ventricular septal defects may be more reliably and easily identified with the use of color flow
Doppler ultrasound.
Interest continues to focus on applying three-dimensional (3-D) and four-dimensional (4-D) technologies to
fetal echocardiography. These technologies are becoming more readily available on ultrasound equipment,
and 2-D fetal echocardiography requires considerable
expertise to perform and interpret correctly. The major
drawbacks to applying 3-D/4-D technologies to the
fetal heart have been long acquisition time and the
need for cardiac gating. Recent improvements allow for
almost real-time examination. Current 3-D techniques
depend on the type of equipment used
33-35
and include
spatiotemporal image correlation (STIC), multiplanar
Text continued on p. 1305
Chapter 37 ■ The Fetal Heart 1301
LV
RA
LA
RV
LV
A
RA
RV
LV
P
LA
P
B
RA
RVLA
FIGURE 37-5. Four-chamber view of heart. A, Apical four-
chamber view shows the interatrial and interventricular septa parallel to
the angle of insonation. B, Subcostal four-chamber view shows the interatrial and interventricular septa perpendicular to the angle of insonation.
C, Apical four-chamber view shows the two superior pulmonary veins (P)
C
entering the left atrium (LA); LV, left ventricle; RA, right atrium; RV, right
ventricle.
RA
RV
LV
A
LA
FIGURE 37-6. Continuity of aorta (A) with left ventricle (LV);
LA, left atrium; RA, right atrium; RV, right ventricle.
RV
P
FIGURE 37-7. Continuity of pulmonary artery (P) with right
ventricle (RV).
1302 PART IV ■ Obstetric Sonography
PV
RV
IVS
LV
FIGURE 37-8. Short-axis view of ventricles. Anterior
right ventricle (RV) is normally slightly larger than the left ventricle (LV); IVS, interventricular septum.
PA
RVOT
AO
RA
LA
FF
SP
FIGURE 37-9. Short-axis view of great vessels. Aorta
(AO) in center with pulmonary artery (PA) draping anteriorly;
RVOT, right ventricular outflow tract; LA, left atrium; RA, right
atrium; PV, pulmonic valve; FF, foraminal flap; SP, spine.
LV RV
A
RALA
SP
FIGURE 37-10. Apical five-chamber view shows continuity
of the aorta (A) with the left ventricle (LV); LA, left atrium; RA,
right atrium; RV, right ventricle; SP, spine.
P
A
T>
SP
S
FIGURE 37-11. Three-vessel and trachea view shows the
correct orientation of the main pulmonary artery–ductus arteriosus confluence (P), the transverse aortic arch (A), and the superior
vena cava (S). This view also shows the two great vessels correctly
positioned on the left side of the trachea (T). SP, Spine.
Chapter 37 ■ The Fetal Heart 1303
AO
LS
LC
I
FIGURE 37-12. Normal aortic arch. Sagittal view shows
the rounded, “candy cane” appearance of aortic arch and the head
and neck vessels arising from it; LS, left subclavian artery; LC, left
carotid artery; I, innominate artery; AO, descending aorta.
PA
A
D
LA
AO
FIGURE 37-13. Normal ductal arch. Sagittal view shows
pulmonary artery (PA) draping over the aorta (A) and joining the
ductus arteriosus (D), which then joins the descending aorta (AO);
LA, left atrium.
LV
LA
V V V V V V V
A A A A A A APA
PV
–
RV
RA
FIGURE 37-15. Using M-mode echocardiography
to analyze an arrhythmia: conducted premature
atrial contractions. The cursor is placed simultaneously
through the left ventricle (LV) and right atrium (RA). The
M-mode tracing shows normal atrial beats (A) followed by a
premature atrial contraction (PA). The ventricles show normal
ventricular contraction (V) following each atrial beat and a premature beat (PV) following the premature atrial contraction. LA,
Left atrium; RV, right ventricle.
1.0 sec
1 cm
RV
AO
LA PL
A
AL
ClosedOpen
F F
TV
IVS
MV
B
FIGURE 37-14. M-mode echocardiography. A, M-mode tracing through the aortic root shows the aortic valve opening and
closing. The foraminal flap can be seen opening into the left atrium (LA). RV, Right ventricle; AL, anterior leaflet of aortic valve; PL,
posterior leaflet of aortic valve. B, M-mode tracing shows opening and closing of the mitral valve (MV) and tricuspid valve (TV); IVS,
interventricular septum.
1304 PART IV ■ Obstetric Sonography
LVRV
RA LA
RA
RV
SP
A
A
A
A
E
E
E
E
A
A
A
E
E
E
FIGURE 37-16. Spectral Doppler ultrasound used
to interrogate a normal mitral valve. Spectral Doppler
sample volume is placed distal to the mitral valve in the left ventricle (LV). A normal mitral valve waveform is appreciated above
the baseline, showing the normal early diastolic (E) and atrial
contraction (A) wave points. LA, Left atrium; RA, right atrium;
RV, right ventricle; SP, spine.
Vel 519 cm/s
PG 108 mmHg
R R
T T T T
R R R
FIGURE 37-17. Tricuspid insufficiency. Spectral
Doppler sample volume is placed proximal to the tricuspid valve
in the right atrium (RA). The regurgitant flow (R) can be seen
above the baseline. This implies that the valve has not closed
completely during systole, and therefore blood flow is retrograde
into the right atrium. RV, Right ventricle.
D
AA
PA
A
B
FIGURE 37-18. Using color Doppler ultrasound to access normal blood flow. A, Color Doppler ultrasound shows
normal flow through the pulmonary artery (PA). B, Color Doppler ultrasound to access normal blood flow through the aortic arch (AA)
and descending aorta (D). Note that flow is continuous through the descending aorta, but due to angle of 0 degrees in the middle of the
image, an artifact gives the appearance of narrowing, and the color of flow changes from red to blue.
Chapter 37 ■ The Fetal Heart 1305
4 wks
Septum primum
RT LT
Atrium
A B
RT LT
Ostium primum
Endocardial
cushion
5 wks
Septum secundum
Septum primum
Ostium secundum
RT LT
RA LA
1
/
wks
4
2
Developing
ostium secundum
Ostium primum
Endocardial
cushion
8 wks
RT LT
C
Septum secundum
Foramen ovale
Foraminal flap
1
4
/
– 5 wks
2
Ostium secundum
Ostium primum
D E
FIGURE 37-19. Development of intra-atrial septum (viewed facing patient). A, At 4 weeks’ gestation the septum
primum is small. A large ostium primum is present. B, At 4.5 weeks, enlargement of the septum primum results in reduction in size of
the ostium primum. Perforations in the septum primum develop. C, Perforations in the septum primum coalesce to form the ostium
secundum. D, At 5 weeks the septum primum has fused to the endocardial cushions, and the septum secundum begins to develop to the
right of the septum primum. E, At 8 weeks the septum secundum has enlarged, now covering the ostium secundum. Blood flows from
the right atrium through the valve mechanism (foraminal flap) of the foramen ovale.
reconstruction, tissue Doppler gating, inversion mode,
and matrix array real-time 3-D. Because of various limitations associated with all these technologies, 3-D fetal
echocardiography should always be used as an adjunct
to standard 2-D ultrasound. Limitations include fetal
motion artifact, equipment limitations (based on manufacturer), and decreased resolution of rendered images.
STRUCTURAL ANOMALIES
Atrial Septal Defect
An atrial septal defect (ASD) results from an error in the
amount of tissue resorbed or deposited in the interatrial
septum. It is the fifth most common form of congenital
heart disease and is the most common form in adult
patients.
comprise 6.7% of CHD in live-born infants.
occur twice as often in females as males.
associated with a variety of cardiac, extracardiac, and
chromosomal abnormalities. ASDs can be classified by
embryogenesis, size, or relationship to the fossa ovalis.
of gestation, the primitive atrium is divided into right
and left halves. The septum primum, a crescent-shaped
membrane, develops along the cephalad portion of the
atrium and grows caudally toward the endocardial
cushions. The space between these two structures,
termed the ostium primum, disappears when the septum
primum fuses with the endocardial cushion. Before
complete fusion, however, multiple small fenestrations
36,37
ASDs occur in 1 per 1500 live births
36
40,41
ASDs are
38,39
and
ASDs
Embryologically, between the fourth and sixth weeks
develop in the septum primum, coalescing to form the
ostium secundum. A second crescent-shaped membrane subsequently develops just to the right of the
septum primum. As this membrane grows toward the
endocardial cushion, it partially covers the ostium secundum. Its crescent-shaped lower border never entirely
fuses with the endocardial cushion, leaving an opening,
the foramen ovale (Fig. 37-19).
Ostium secundum ASDs make up more than 80%
of all ASDs and generally occur in isolation. This ASD
is caused by excessive resorption of the septum primum
(foraminal flap) or by inadequate growth of the septum
secundum (Fig. 37-20, A). The ostium primum ASD
is the second most common type and is located low in
the atrial septum, near the atrioventricular (A-V) valves.
Although the ostium primum ASD may occur alone, it
is more frequently associated with a more complex congenital cardiac anomaly, the atrioventricular septal
defect (Fig. 37-20, B).
The sinus venosus ASD is a rare defect that can
be divided into two types: (1) sinus venosus ASD of
the superior vena cava (SVC), with the defect adjacent
to the SVC, and (2) sinus venosus ASD of the inferior
vena cava (IVC), with the defect adjacent to the IVC.
The first type is often associated with anomalous pul-
monary venous return (Fig. 37-20, C).
The prenatal sonographic diagnosis of ASD is difficult
because the normal patent foramen ovale, which allows
blood to flow from the right to the left atrium in utero,
itself represents an ASD. It can be difficult to distinguish
a small, pathologic ASD from the normal patent foramen
ovale. The foraminal flap, or septum primum, is clearly
1306 PART IV ■ Obstetric Sonography
SVC SVC
SVC
RA
RA
RV
IVC IVC
Ostium secundum ASD Ostium primum ASD Sinous venosus ASD
A
FIGURE 37-20. Types of atrial septal defect (ASD). Schema of the atrial septum viewed from the right atrium. A, Ostium
secundum ASD. B, Ostium primum ASD. C, Sinus venosus ASD.
B C
visualized on the four-chamber view. It has a “loose
pocket” configuration, appearing either circular or linear
in shape as it opens into the left atrium
42,43
(Fig. 37-21).
The septum secundum, which is thick and relatively
stationary, makes up the majority of the atrial septum.
The foramen ovale is an opening in the septum secundum. The septum secundum and foramen ovale are
well visualized in the four-chamber views. The maximal
size of the normal foramen ovale differs by 1 mm or less
from the aortic root diameter at all gestational ages.44 An
ostium secundum ASD appears as a larger than expected
defect in the central portion of the atrial septum near the
foramen ovale. Alternatively, it can appear as a deficient
foraminal flap.
If the lowest portion of the atrial septum (just adjacent
to the A-V valves) is deficient, an ostium primum defect
should be suspected (Fig. 37-22). Color Doppler ultrasound may be helpful in the diagnosis of larger ASDs.
However, small ASDs are commonly obscured by the
normal flow through the patent foramen ovale.
45,46
A large, right-to-left shunt is physiologic in utero, and
thus an ASD generally does not compromise the fetus
hemodynamically. After birth, the shunt may cause right
ventricular overload and pulmonary hypertension. Spontaneous closure of an ASD will occur in approximately
two thirds of cases.
remain asymptomatic into their fifties.
47
Patients with small ASDs may
48
RV
IVC
defects also involve a portion of the muscular septum,
they are usually referred to as perimembranous defects.
The subcostal four-chamber view provides optimal evaluation of the interventricular septum. At sonography, a
VSD appears as an area of discontinuity in the interventricular septum. When the defect is small, this diagnosis
is problematic, and at least one third of VSDs are missed
on the four-chamber view.
sound imaging may improve the diagnostic accuracy for
VSD. However, most are missed on fetal echocardiogra-
45,56,57
phy.
cardiography may be documented with color Doppler
ultrasound
Small VSDs not detectable on gray-scale echo-
30
(Fig. 37-24). In the setting of an isolated
VSD, color Doppler ultrasound imaging typically shows
bidirectional interventricular shunting, with a systolic
right-to-left shunt and a late diastolic left-to-right shunt.
The prognosis for an infant with an isolated VSD
is excellent, and many such defects go undetected.
About 40% of VSDs close in the first year of life,
and 60% resolve by 5 years of age.
defects detected in the fetus are associated with an 84%
mortality.
61
Concurrent cardiac, extracardiac, and chromosomal anomalies (trisomy 13, 18, 21, and 22) are
associated with a worse prognosis.
Ventricular septal defects may be extremely difficult
to diagnose in utero, particularly when small in size.
Additionally, many small VSDs will close in utero or
RA
15,45,52-56
RV
Color Doppler ultra-
58-60
However, large
shortly after birth. A “pseudo” VSD in the membranous
Ventricular Septal Defect
Isolated ventricular septal defect (VSD) is the most
common cardiac anomaly, accounting for 30% of heart
defects diagnosed in live-born infants and 9.7% diagnosed in utero.
cardiac anomalies in half the cases.
36,37,49
VSDs are associated with other
50
Of the structural
cardiac defects, VSDs have the highest recurrence rate
and the highest association with teratogen exposure.
They are classified according to their position in the
interventricular septum (Fig. 37-23) as membranous or
muscular VSD (inlet, trabecular, outlet).
About 80% of VSDs occur in the membranous portion
of the septum.
51
However, because most membranous
50
portion of the septum may be appreciated when evaluating the interventricular septum from an apical fourchamber view. This occurs when the angle of insonation
is parallel to the septum, causing an artifactual dropout
of the thin, membranous septum.
Atrioventricular Septal Defect
Atrioventricular septal defect (AVSD) refers to a spectrum of cardiac abnormalities involving various degrees
of deficiency of the interatrial and interventricular septa
and of the mitral and tricuspid valves. These defects arise
when the endocardial cushions fail to fuse properly and
were previously called endocardial cushion defects or
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