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Chapter 43 ■ Fetal Surveillance: Doppler Assessment of Pregnancy and Biophysical Profile 1477
trimester,11 and the diastolic component increases with
advancing gestation because of a decreased placental vascular resistance.
25,36,37
Absent end diastolic flow in the
umbilical artery is an abnormal finding by the mid–
second trimester. UA waveforms should be obtained
during periods of fetal apnea because fetal breathing
affects the waveforms (Fig. 43-7). Similarly, a fetal
cardiac arrhythmia, particularly periods of bradycardia,
can also lead to abnormal Doppler ultrasound indices.
In pathologic conditions such as IUGR, the UA waveforms change, with a decreased diastolic component, and
the angle-independent indices become abnormal, with
values above their reference ranges.
reflect an increased placental vascular resistance.
38-42
These changes
25
As the
placental insufficiency worsens, the diastolic velocity
decreases, then becomes absent, and later is reversed.
Some fetuses have a decreased diastolic velocity that
remains constant with advancing gestation and never
becomes absent or reversed, which may be caused by a
milder form of placental insufficiency. Trudinger et al.25
demonstrated that the number of placental arteries
per high-power field is decreased in cases of abnormal
UA Doppler ultrasound.
25
Only in pregnancies with
suspected IUGR or hypertensive disease of pregnancy
does the use of UA Doppler ultrasound reduce the
number of perinatal deaths and unnecessary obstetric
interventions.
43
Middle Cerebral Artery
Anteriorly, the circle of Willis is composed of the anterior cerebral arteries (branches of internal carotid artery
[ICA] connected by anterior communicating artery);
posteriorly, it consists of the two posterior cerebral arteries (branches of basilar artery connected on either side
to ICA), which supply the cerebral hemispheres on each
side. These arteries have different waveforms,
44
so it is
important to know which artery is being interrogated.
The middle cerebral artery is the vessel of choice to
assess the fetal cerebral circulation because it is easy to
identify, is highly reproducible, and provides information on the brain-sparing effect.
26
In addition, the MCA
can be studied easily with an angle of 0 degrees between
the ultrasound beam and the direction of blood flow
(Fig. 43-8), providing information on the true velocity
of the blood flow.
after its origin from the ICA.
26
The MCA should be sampled soon
17
Technique is important
for obtaining accurate results. In the absence of fetal
breathing and movements, the examination takes
approximately 5 to 10 minutes with the patient.
Reference values for the middle cerebral artery pul-
satility index (MCA PI) change throughout gestation
(Table 43-1 and Fig. 43-9). The lower PI values early
and late in gestation may be caused by the increased
metabolic requirements of the brain during these
periods.
45
Several conditions are associated with an
PSV
44.8 cm/s
EDV
8.12 cm/s
MDV
8.12 cm/s
RI
PI
S/D
TAPV
HR
FIGURE 43-5. Umbilical artery waveform near pla-
cental insertion.
0.82
1.68
5.5
21.9 cm/s
147 bpm
FIGURE 43-7. Umbilical artery waveforms. UA
Doppler ultrasound waveforms during fetal breathing are different
from each other. (From Mari G, Detti L. Doppler ultrasound:
application to fetal medicine. In Fleischer AC, Manning FA, Jeanty
P, Romero R, editors. Sonography in obstetrics and gynecology:
principles and practice. New York, 2001, McGraw-Hill, pp
247-283.)
A B
FIGURE 43-6. Umbilical artery (UA) in intrauterine growth restriction (IUGR). A, Reversal of diastolic flow. UA
Doppler waveforms obtained in fetus with severe IUGR, 23 days before fetal demise at 26 weeks’ gestation. The umbilical cord was
sampled in a free-floating segment. B, Absent, but not reversed, UA diastolic flow on Doppler ultrasound waveforms sampled at the
placental insertion. (From Mari G. Doppler ultrasonography in obstetrics: from the diagnosis of fetal anemia to the treatment of intrauterine
growth-restricted fetuses. Am J Obstet Gynecol 2009;200:613 e1-e9.)
1478 PART IV ■ Obstetric Sonography
A B
FIGURE 43-8. Middle cerebral artery (MCA) on color Doppler ultrasound. A, Circle of Willis. B, Spectral Doppler
tracing. Note how Doppler gate is on the MCA just after the origin from the internal carotid artery. Note that the MCA is studied with
an angle close to 0 degrees; therefore the velocity is close to the real velocity of the blood flow. (From Mari G, Abuhamad AZ, Cosmi E,
et al. Middle cerebral artery peak systolic velocity: technique and variability. J Ultrasound Med 2005;24:425-430.)
MEASUREMENT OF MIDDLE CEREBRAL
ARTERY (MCA) PEAK SYSTOLIC
VELOCITY (PSV)
1. Obtain an axial section of the head at the level
of the sphenoid bones.
2. Use color Doppler ultrasound to identify circle of
Willis with MCA at angle close to 0 degrees.
3. Enlarge image of MCA.
4. Interrogate MCA soon after its origin from the
ICA at angle close to 0 degrees using a 1- to
2-mm sample volume.
5. Measure PSV.
6. Repeat the collection of MCA Doppler
ultrasound three to five times.
7. Repeated waveforms should be similar.
increase or decrease of the MCA PI when compared to
normal values.
Animal and human experiments have shown that
IUGR is associated with increased blood flow to the fetal
46,47
brain.
be demonstrated by Doppler ultrasound of the MCA.
This increase in blood flow during diastole can
26
This effect is termed the brain-sparing effect and is
demonstrated by a lower value of the MCA PI (Fig.
43-10). It is important to emphasize that the MCA PI
changes with increasing gestational age. In IUGR fetuses
with a PI below the normal range, there is a greater
incidence of adverse perinatal outcome.
sparing effect may be transient, as reported during prolonged hypoxemia in animal experiments,
be lost in the overstressed human fetus
26
The brain-
48
and it may
49
(Fig. 43-11).
The MCA PI is below the normal range when oxygen
tension (Po
) is reduced.50 Maximum reduction in PI is
2
TABLE 43-1. MIDDLE CEREBRAL
ARTERY PULSATILITY INDEX (MCA PI)*
Normal Values
GA (week)
15 0.99 1.57 2.14
16 1.08 1.71 2.33
17 1.16 1.83 2.51
18 1.23 1.95 2.67
19 1.30 2.05 2.81
20 1.35 2.14 2.93
21 1.40 2.22 3.04
22 1.44 2.29 3.13
23 1.48 2.34 3.20
24 1.51 2.38 3.26
25 1.52 2.41 3.30
26 1.54 2.43 3.32
27 1.54 2.44 3.33
28 1.54 2.43 3.32
29 1.52 2.41 3.30
30 1.50 2.38 3.26
31 1.48 2.34 3.20
32 1.44 2.28 3.12
33 1.40 2.21 3.03
34 1.35 2.13 2.92
35 1.29 2.04 2.79
36 1.22 1.94 2.65
37 1.15 1.82 2.49
38 1.07 1.69 2.32
39 0.98 1.56 2.13
40 0.89 1.40 1.92
41 0.78 1.24 1.70
42 0.67 1.06 1.45
From Mari G, Deter RL. Middle cerebral artery flow velocity waveforms in
normal and small-for-gestational-age fetuses. Am J Obstet Gynecol
1992;166:1262-1270.
*PI = −1.9763 + (0.32737 GA1) + (−0.00611 GA2).
†Predicted value − (2 × 0.184 × Predicted value).
‡Predicted value + (2 × 0.184 × Predicted value).
GA, Gestational age.
LOWER
LIMIT†
PREDICTED
VALUE UPPER LIMIT‡
Chapter 43 ■ Fetal Surveillance: Doppler Assessment of Pregnancy and Biophysical Profile 1479
15 weeks
69
34
0
18 weeks
42
0
24 weeks
46
0
1 sec
29 weeks
54
0
36 weeks
104
cm/sec
0
39.2 weeks
91
0
FIGURE 43-9. Middle cerebral artery. MCA Doppler ultrasound at various gestational ages shows how diastolic flow increases
as gestation advances. (From Mari G, Deter RL. Middle cerebral artery flow velocity waveforms in normal and small-for-gestational-age fetuses.
Am J Obstet Gynecol 1992;166:1262-1270.)
FACTORS ASSOCIATED WITH LOW
AND HIGH MIDDLE CEREBRAL
ARTERY PULSATILITY INDEX
(MCA PI) VALUES
LOW MCA PI
Brain growth spurt
Postuterine contractions
High fetal heart rate
Severe anemia
Post-transfusion
Therapeutic amniocentesis
Ductal constriction and tricuspid insufficiency
Hypoxemia and acidemia
HIGH MCA PI
Uterine contractions
Low fetal heart rate
Oligohydramnios
Fetal head compression
Sustained hypoxemia with acidemia
Hydranencephaly
Indomethacin administration
Modified from Mari G, Detti L. Doppler ultrasound:
application to fetal medicine. In Fleischer AC, Manning
FA, Jeanty P, Romero R, editors. Sonography in obstetrics
and gynecology: principles and practice. New York, 2001,
McGraw-Hill, pp 247-283.
0
FIGURE 43-10. Middle cerebral artery. MCA Doppler
ultrasound in IUGR at 24 weeks’ gestation shows how the brainsparing effect has resulted in relatively high diastolic flow (compare
to 24 weeks in Fig. 43-9). The MCA pulsatility index (PI) is
abnormal at 24 weeks. (From Mari G, Detti L. Doppler ultrasound:
application to fetal medicine. In Fleischer AC, Manning FA, Jeanty
P, Romero R, editors. Sonography in obstetrics and gynecology:
principles and practice. New York, 2001, McGraw-Hill, pp
247-283.)
reached when the fetal Po2 is 2 to 4 standard deviations
(SD) below normal for gestational age. When the O
deficit is greater, the PI tends to rise, which presumably
reflects the development of brain edema. In growthrestricted fetuses the disappearance of the brain-sparing
effect or presence of reversed MCA flow is a critical event
for the fetus and precedes fetal death.
49,51-53
Reversed
2
1480 PART IV ■ Obstetric Sonography
25 weeks Umbilical artery
27 weeks
55
0
Middle cerebral artery
70
0
FIGURE 43-11. Umbilical artery (UA) and middle cerebral artery (MCA) waveforms in severe IUGR. At 25
weeks’ gestation, there was absent end diastolic flow of the UA, pulsation of the umbilical vein, and the brain-sparing effect, as shown by
high diastolic flow of the MCA. At 27 weeks, there was reverse diastolic flow of the UA, and the brain-sparing effect was not present.
The fetus died 24 hours after this study. (From Mari G, Wasserstrum N. Flow velocity waveforms of the fetal circulation preceding fetal death
in a case of lupus anticoagulant. Am J Obstet Gynecol 1991;164:776-778.)
A B
C D
FIGURE 43-12. Pulsatility index (PI) and peak systolic velocity (PSV) in IUGR. A, PI is abnormal, but PSV is normal.
B, Both PI and PSV are abnormal. These findings indicate a more severe IUGR condition than in cases with normal PSV. C, Middle
cerebral artery (MCA) waveforms with absent end diastolic flow. D, Reversed flow in MCA. (A and B from Mari G, Hanif F. Intrauterine
growth restriction: how to manage and when to deliver. Clin Obstet Gynecol 2007;50:497-509. C and D from Mari G. Doppler ultrasonography
in obstetrics: from the diagnosis of fetal anemia to the treatment of intrauterine growth-restricted fetuses. Am J Obstet Gynecol 2009;200:
613 e1-e9.)
flow of the MCA velocity waveforms can be observed
with head compression in normal pregnancies.
The middle cerebral artery peak systolic velocity
(MCA PSV) is increased in IUGR fetuses (Fig. 43-12).
This increase predicts perinatal mortality more accurately than does the MCA PI.
explained because initially the MCA PI is abnormal in
most IUGR fetuses but subsequently increases and
trends toward normalization before delivery or fetal
22
This finding can be
death. Conversely, the MCA PSV progressively increases
with advancing gestation in all fetuses and tends to
decrease slightly just before fetal biophysical deterioration or fetal demise. Despite this decrease, however, the
MCA PSV value remains above the upper limit of
normal until a few hours before delivery or fetal demise.
Although the MCA PSV is increased in anemic
fetuses, those with IUGR are not anemic, raising the
question, what is the mechanism of increased MCA PSV
Chapter 43 ■ Fetal Surveillance: Doppler Assessment of Pregnancy and Biophysical Profile 1481
A B
FIGURE 43-13. Descending aorta. A, At the level of the diaphragm. B, Distal to the origin of the renal arteries. (From Mari G,
Detti L. Doppler ultrasound: application to fetal medicine. In Fleischer AC, Manning FA, Jeanty P, Romero R, editors. Sonography in obstetrics
and gynecology: principles and practice. New York, 2001, McGraw-Hill, pp 247-283.)
in anemic and nonanemic fetuses? Hanif et al.54 showed
that the mechanisms determining increased MCA PSV
values are different in anemic AGA fetuses compared
with nonanemic IUGR fetuses.
54
In anemic fetuses the
high MCA PSV is related to a decreased fetal hemoglobin that can decrease blood viscosity; therefore cardiac
output increases. In IUGR fetuses, however, the MCA
PSV increase is significantly related to hypoxemia and
hypercapnia and thus to brain autoregulation.
17,54
Splenic
Celiac
Other Arteries
Many other arteries have been examined in AGA fetuses
and those with IUGR, increasing our understanding of
fetal physiology and pathophysiology in these conditions. In our experience, however, the study of these
vessels as currently performed adds no new information
to the study of the UA and MCA in the management of
IUGR fetuses.
Descending Aorta. Waveforms from the fetal descending aorta are usually recorded at the level of the diaphragm. Waveforms distal to the origin of the renal
arteries are different
descending aorta is 1.96 ± 0.30 (SD) at the diaphragm
and 1.68 ± 0.28 after the origin of the renal arteries.
55,56
(Fig. 43-13). The PI of the fetal
56
The pulsatility index is the preferred measurement in the
descending aorta because end diastolic flow may be
absent in normal fetuses. Waveforms in the descending
aorta represent the summation of flow to the kidneys,
bowel, placenta, and lower extremities. The PI of the
fetal descending aorta remains relatively constant
throughout gestation because placental and renal resistance decreases while lower extremity vascular resistance
increases with advancing gestation.
57
In severe IUGR
fetuses, there is reversed flow in the descending aorta.
AO
FIGURE 43-14. Celiac trunk. Transverse section of the fetal
abdomen at the level of the descending aorta, celiac trunk, splenic
artery, and hepatic artery. (From Abuhamad AZ, Mari G, Bogdan
D, Evans AT 3rd. Doppler flow velocimetry of the splenic artery in
the human fetus: is it a marker of chronic hypoxia? Am J Obstet
Gynecol 1995;172:820-825.)
Splenic Artery. The celiac trunk arises from the aorta
between the crura of the diaphragm at the level of the
12th thoracic vertebra (Fig. 43-14). The celiac trunk
has three main branches: the splenic, common hepatic,
and left gastric arteries. Abuhamad et al.58 found that
IUGR fetuses have a lower splenic artery PI value. This
1482 PART IV ■ Obstetric Sonography
suggests that in cases of chronic hypoxia, there is
increased blood flow to the spleen because of increased
erythropoiesis.
59,60
Superior Mesenteric Artery. Superior mesenteric
artery fetal waveforms are shown in Fig. 43-15. PI values
increase over time.
61
This may reflect increased bowel
resistance because of increased bowel length with advancing gestation. However, assessment of these waveforms
has not been found to be useful in evaluating IUGR
62
fetuses.
Adrenal Artery. In IUGR fetuses, there is a lower
adrenal artery PI, suggesting an adrenal “stress response,”
as reported in animal studies
63
(Fig. 43-16).
Renal Artery. The renal artery can be studied in a
coronal section of the descending aorta and after its
origin from the descending aorta in the kidneys (Fig.
43-17). Doppler ultrasound waveforms of the renal
artery and vein are displayed on either side of the baseline. The PI must be used to assess the renal artery
because EDV is often absent in the second trimester and
early third trimester.
64,65
In fetuses with severe IUGR,
the renal artery PI is above the reference range.
Femoral, Internal Iliac, and External Iliac Arteries. Femoral artery waveforms are obtained soon after
the vessel origin (Fig. 43-18). The normal appearance of
the femoral artery waveforms changes during gestation.
There is no difference between the femoral artery PI and
the external iliac artery PI.
57
The internal iliac artery is
the intra-abdominal continuation of the umbilical artery
and therefore reflects the UA waveforms.
Superior Cerebellar Artery. The superior cerebellar
artery arises from the basilar artery before it divides
into the two posterior cerebral arteries. The PI of the
superior cerebellar artery is similar to that of the MCA.
Uerpairojkit et al.66 found that the PI of the superior
cerebellar artery is lower than normal in IUGR fetuses,
whereas it is in the normal range in SGA fetuses.
Fetal Venous System
Most studies on fetal venous blood flow have been performed on the blood flow from the placenta, which
returns to the heart through the umbilical vein. Normal
flow in the free-floating umbilical vein is monophasic
(see Fig. 43-3). Fetuses with pulsation in the umbilical
vein in the second and third trimesters have a higher
morbidity and mortality, even in the setting of normal
UA blood flow. For the umbilical vein, we use a qualitative assessment: continuous versus pulsatile blood
67,68
flow
(Fig. 43-19).
Flow from the umbilical vein enters the fetal abdomen
and at the portal sinus enters the ductus venosus (Fig.
43-20) and inferior vena cava. Approximately 50% of
the blood flow from the umbilical vein goes to the liver
and 50% to the DV.
tinuous flow that becomes pulsatile at the portal sinus
(Fig. 43-21). The IVC, before its entrance into the right
atrium, has a triphasic pulsatile pattern.
69,70
The umbilical vein has a con-
73,74
The first
71,72
forward wave begins to increase with atrial relaxation,
reaches a peak during ventricular systole, and then falls
to a nadir at the end of ventricular systole. The second
SMA
AO
SMA PI = 2.91 AO PI = 1.5
FIGURE 43-15. Superior mesenteric artery (SMA)
and descending aorta (AO). The sample volume was
initially placed on the SMA and then moved to the AO; PI,
pulsatility index. (From Mari G, Detti L. Doppler ultrasound:
application to fetal medicine. In Fleischer AC, Manning FA, Jeanty
P, Romero R, editors. Sonography in obstetrics and gynecology:
principles and practice. New York, 2001, McGraw-Hill,
pp 247-283.)
A B
FIGURE 43-16. Adrenal artery. A, Appropriate-for-gestational-age (AGA) fetus. B, Fetus with IUGR. (From Mari G, Uerpairojkit
B, Abuhamad AZ, Copel JA. Adrenal artery velocity waveforms in the appropriate and small-for-gestational-age fetus. Ultrasound Obstet Gynecol
1996;8:82-86.)
Chapter 43 ■ Fetal Surveillance: Doppler Assessment of Pregnancy and Biophysical Profile 1483
1
2
CI
CI
RA
RA
DAO
C
D
A
B
A
29 weeks
A
B
73
0
73
0
73
38 weeks
91
0
91
0
91
B
0
C
73
0
D
C
FIGURE 43-17. Renal artery. A, Coronal section of the fetal descending aorta (DAO); RA, renal artery at origin from aorta; CI,
common iliac artery. B, Diagram shows where the waveforms in C were obtained. C, Waveforms of the renal artery obtained at different
levels. (From Mari G, Detti L. Doppler ultrasound: application to fetal medicine. In Fleischer AC, Manning FA, Jeanty P, Romero R, editors.
Sonography in obstetrics and gynecology: principles and practice. New York, 2001, McGraw-Hill, pp 247-283.)
forward wave occurs during early diastole, and the third
wave, characterized by reversed flow, is present in late
diastole with atrial contraction. In healthy fetuses, a significant decrease of the reversed flow during atrial contraction is present with advancing gestation.
74
These
changes are related to improved ventricular compliance
and to the reduction of right ventricular afterload caused
by the fall in placental resistance as gestation advances.
In IUGR fetuses the IVC is characterized by an increase
in reversed flow during atrial contraction.
74
This increase
is attributed to abnormal ventricular filling characteristics, an abnormal ventricular chamber, or wall compliance (Fig. 43-22).
0
91
0
The ductus venosus transports oxygenated blood from
the umbilical vein to the left atrium and ventricle, then
to the myocardium and brain. The DV waveform has a
biphasic pattern characterized by two peaks: the “S”, or
peak systolic velocity (PSV), which corresponds to the
highest velocity of the blood in systole and is followed
by a period of decreased velocity called isovolumetric
relaxation (IRV); and the “D”, which corresponds to the
rapid filling of the ventricles that is followed by a nadir,
the “A wave,” which corresponds to atrial contraction.
Hemodynamically, these phases reflect the rapid chronologic change in pressure gradients between the umbilical
vein and the right atrium. In AGA fetuses, there is
75
1484 PART IV ■ Obstetric Sonography
55
ABA
B
C
0
57
0
58
0
109
forward flow at the DV, and the PI for veins ([S − D]/A)
decreases with advancing gestation. In the first trimester,
reversed blood flow may be caused by the immaturity of
the sphincter of the DV, which also may explain the
umbilical vein pulsatile pattern seen in the first trimes-
76
A common error is sampling the left hepatic vein
ter.
rather than the DV. The left hepatic vein waveform is
similar to that of the IVC and has reversed flow in AGA
fetuses.
In growth-restricted fetuses, the PI increases in the
DV, and in the most severe cases, there is A wave of
reversed flow. The presence of DV reversed flow can be
explained in light of the transitional phase recently
described by Picconi et al.77 Based on this study, when
the DV is longitudinally assessed in IUGR fetuses, the
progression follows three steps: (1) normal waveforms,
(2) a period with normal and abnormal waveforms, and
(3) persistent abnormal waveforms. Picconi et al.78 also
recently developed the S-wave/isovolumetric A-wave
(SIA) index for the analysis of the DV waveforms (Fig.
43-23), which allows a much more accurate prediction
of fetal outcome compared to A-wave reversed flow
78
(Fig. 43-24).
alone
0
D
FIGURE 43-18. Femoral artery. A, Forward diastolic flow
in femoral artery at 18 weeks’ gestation. Presence of a notch at B,
24 weeks, and C, 30 weeks. D, Reversed flow at 39 weeks. (From
Mari G. Arterial blood flow velocity waveforms of the pelvis and lower
extremities in normal and growth-retarded fetuses. Am J Obstet
Gynecol 1991;165:143-151.)
A
Fetal Cardiac System
Atrioventricular Valves. Atrioventricular (A-V) valve
(mitral and tricuspid) velocities may be obtained from a
four-chamber view by placing the sample volume just
distal to the valve leaflets. Two peaks usually are present
in the A-V valve signal; the first peak reflects passive
ventricular filling in early diastole (E), and the second
peak reflects the atrial contraction in late diastole (A).
Early in gestation, A is much higher than E
79,80
(see
Fig. 37-25), indicating that the atrial contraction is
B
C
FIGURE 43-19. Abnormal umbilical vein waveforms. A, Single pulsation. B, Double pulsation. Waveforms obtained close
to the origin of the ductus venosus 48 hours before fetal demise. C, Double pulsation; same case as B. Waveforms obtained between the
origin of the ductus venosus and the umbilicus. D, Reversed flow. Fetus died within 24 hours of this finding. (From Mari G, Hanif F,
Kruger M. Sequence of cardiovascular changes in IUGR in pregnancies with and without preeclampsia. Prenat Diagn 2008;28:377-383.)
D
Chapter 43 ■ Fetal Surveillance: Doppler Assessment of Pregnancy and Biophysical Profile 1485
.50
S
D
UV
LSHV
DV
A
IVC
B
IRV
a
C
FIGURE 43-20. Ductus venosus. A, Sagittal section of fetal torso. The ductus venosus (DV) is brighter than the other vascular
areas because of the high blood velocity at this point. When the DV is not clearly visualized, this brighter appearance helps to distinguish
the DV from the surrounding vessels. UV, Umbilical vein; IVC, inferior vena cava; LHV, left hepatic vein. B, Normal DV waveforms: S,
peak systolic velocity; D, first phase of diastole corresponding to the passive rapid filling of the ventricles; IRV, isovolumetric relaxation;
a, second phase of diastole with atrial contraction. C, DV waveforms obtained at 24 weeks’ gestation. Note that there is reversal of flow.
(From Mari G. Doppler ultrasonography in obstetrics: from the diagnosis of fetal anemia to the treatment of intrauterine growth-restricted fetuses.
Am J Obstet Gynecol 2009;200:613 e1-e9.)
.10
m/s
.30
FIGURE 43-21. Normal portal sinus with pulsatile
flow. (From Mari G, Detti L. Doppler ultrasound: application to
fetal medicine. In Fleischer AC, Manning FA, Jeanty P, Romero R,
editors. Sonography in obstetrics and gynecology: principles and
practice. New York, 2001, McGraw-Hill, pp 247-283.)
m/s
FIGURE 43-22. Abnormal inferior vena cava wave-
form. These values were obtained 48 hours before intrauterine
fetal demise. Note the double-reversed flow. (From Mari G, Hanif
F, Kruger M. Sequence of cardiovascular changes in IUGR in pregnancies with and without preeclampsia. Prenat Diagn 2008;28:
377-383.)
P
S
I
V
R
V
SIA index = [PSV / (EDV + IRV)]
E
D
P
V
D
V
FIGURE 43-23. Measuring the S-wave/isovolumet-
ric relaxation + A-wave (SIA) index. Top, Sagittal
section of the fetal body shows the venous vestibulum at the
confluence of the inferior vena cava, ductus venosus, and right
suprahepatic vein. The sample volume is placed in the DV.
Bottom, DV waveform. SIA index = PSV/(EDV − IRV). (From
Picconi JL, Kruger M, Mari G. Ductus venosus S-wave/isovolumetric
A-wave (SIA) index and A-wave reversed flow in severely premature
growth-restricted fetuses. J Ultrasound Med 2008;27:1283-1289.)
important in the fetus. With advancing gestation, early
diastole E increases and reaches late diastole A, suggesting that the atrial systole becomes less important with
maturation of the ventricular myocardium.
79,81-84
At
birth and after birth, E becomes higher than A, suggesting a less important role for atrial contraction. The index
used most to quantify these waveforms is the early-
diastole-to-late-diastole (E/A) ratio. When the A-V
1486 PART IV ■ Obstetric Sonography
RA LA
TV
E A
TR
FIGURE 43-25. Tricuspid regurgitation. Tricuspid
valve (TV) antegrade flow (above baseline) and tricuspid regurgitation (TR; below baseline); RA, right atrium; LA, left atrium; E, E
wave; A, A wave. (From Mari G, Hanif F, Kruger M. Sequence of
cardiovascular changes in IUGR in pregnancies with and without
preeclampsia. Prenat Diagn 2008;28:377-383.)
FIGURE 43-24. Ductus venosus waveforms in IUGR.
At 16 days (top), 4 days (middle), and 24 hours (bottom) before
intrauterine death at 23 weeks’ gestation. The patient declined
intervention because of a fetal weight less than 500 grams and a
gestational age of 23 weeks. Note the reversed flow in the A wave
that becomes more pronounced closer to the time of fetal demise.
(From Picconi JL, Kruger M, Mari G. Ductus venosus S-wave/isovolumetric A-wave (SIA) index and A-wave reversed flow in severely
premature growth-restricted fetuses. J Ultrasound Med 2008;27:
1283-1239.)
valve velocity waveforms are studied at a low incident
angle, the blood velocity obtained is close to the true
velocity. The increase of the E/A ratio with advancing
gestation is a sign of progressive improvement in myocardial compliance. Importantly, with advancing gestation, the peak velocity of the late diastolic A wave does
not change, whereas the peak velocity of the early diastolic E wave increases.
In growth-restricted fetuses, the E/A ratio is higher
than that of normal fetuses controlled for gestational age.
These changes are attributed to changes in preload
without impairment in fetal myocardial diastolic function. In the most severe cases, there is tricuspid and
mitral regurgitation
85
(Fig. 43-25).
Aortic and Pulmonary Valves. Aortic valve (AoV) and
pulmonary valve (PuV) velocities are studied at the levels
of their respective outflow tracts. The peak velocity of
both valves increases with advancing gestation.
86
In
IUGR fetuses the AoV and PuV decrease, which may be
secondary to increased placental resistance.
Measurement of Fetal Cardiac Output. Many investigators have attempted volumetric studies at the level
of the fetal heart,
86-91
based on the formula Q = TVI ×
HR × A, where Q is the absolute flow per minute, TVI
is the time velocity integral, HR is fetal heart rate, and
A is the area of the valve.
The velocity of blood passing through a valve is not
constant, but rather changes with the cardiac cycle;
therefore the TVI, integral to the velocity waveforms
over the entire cardiac cycle, is considered to be a measure
of the length of the column of blood. The main problem
in the calculation of absolute flow per minute (Q) is the
measurement of the valve area. We can assume that the
blood flow at the level of the valvular area is close to
laminar, and that the Doppler spectrum reflects all velocities inside the valve. Newer spectral analyzers in many
ultrasound machines can provide true intensity-weighted
mean flow measurements that take spectral broadening
into account. In addition, we can obtain Doppler ultrasound waveforms with an angle close to 0 degrees (<20
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