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Diagnostic and Clinical Significance of Doppler Ultrasound in Obstetrics
154
Tabelle 17.1 Prospective randomized studies of the clinical significance of Doppler ultrasound in pregnancy.
Lead author n Vascular
Davies (31) 2475 UA + ut CW Screen −m
Mason (76a) 2025 UA CW Screen −m
Whittle (125) 2986 UA CW Screen −m
McParland (78) 509 UA + ut PW H., Rest. −m
Tyrrell (113) 500 UA + ut CW High risk −m
Newnham (83 504 UA + ut CW High risk −m
Trudinger (111) 300 UA CW High risk −m
Hofmeyr (58) 897 UA CW High risk −m
Omtzigt (86) 1598 UA CW High risk +M
Almström (2) 426 UA PW* Rest. +M
UA: Umbilical artery
3
ut: Uteroplacental arteries
CW: Continuous wave Doppler
PW: Pulsed wave Doppler
H: Hypertension
Rest.: Intrauterine growth restriction
−m: Individual clinical management “by best ef fort”
+M: Standardized management according to protocol
*: Without B-mode imaging
Screen: Screening examination
High risk: High risk: Examination for high-risk pregnancy
bed
Doppler
procedure
best judgment into the obstetric management of each
case in the Doppler group. In the control group, by contrast, Doppler readings were either not taken or not
made available. The goal was to discover to what extent Doppler ultrasound influences obstetric management, and whether the consequent interventions (outpatient or inpatient monitoring, aspirin prophylaxis,
stress tests, induction of labor, primary cesarean section, etc.) improve the outcome of the pregnancy
(Newnham et al. 1991, Tyrrell et al. 1990).
Uteroplacental Arteries
Only one study of this type addressing the uteroplacental circulation has been carried out (McParland
et al. 1990). It examined the effectiveness of administering low-dose acetylsalicylic acid (ASA) for an abnormal Doppler finding in the uteroplacental circulation,
known as aspirin prophylaxis. The study population
was confined to nulliparae who had two abnormal
Doppler findings, once at a screening examination at
18 weeks, the second time at a control examination at
24 weeks. The study evaluated the effect of 75 mg ASA
vs. placebo. The study showed that aspirin administered under these conditions reduced preeclampsia
and other hypertensive complications of pregnancy as
well as the rate of subsequent cesarean sections. Blood
loss was comparable in the two groups and there were
no significant side effects. Intrauterine fetal death occurred in three patients with severe hypertension in
Indication
Management
the placebo group, but this incidence did not reach
statistical significance. Thus, in this study the treatment decision was aided by Doppler ultrasound, the
aim being to establish which patients might benefit
from the administration of aspirin.
In some of the clinical studies described in the following section the uteroplacental circulation was examined as well as the umbilical aa., and both findings
were incorporated in the clinical management of the
Doppler group (Davies et al. 1992, McParland and
Pearce 1988, Newnham et al. 1991, Tyrrell et al. 1990).
Umbilical Arteries
Analysis of Individual Clinical Doppler Studies
The first prospective randomized study anywhere of
clinical management using Doppler ultrasound in
high-risk pregnancies was that of Trudinger et al.
(1987). The vessel examined was the umbilical a., and
in the Doppler group the finding was shared with the
responsible obstetrician. The procedure reduced the
frequency of threatened prenatal hypoxemia and the
frequency of secondary cesarean section compared to
the control group. On the other hand, there were no
differences in the duration of gestation, birth weight,
and the frequency of total or elective cesarean sections.
Hence the findings of Doppler sonography of the
umbilical aa. made it easier to detect which infants
would be able to tolerate vaginal delivery and which
would not. Using comparisons from clinical records,
the same workers later found that perinatal mortality
declined significantly in their institution from the time
Doppler ultrasound was introduced in clinical management (Trudinger et al. 1991).
Shortly after that McParland and Pearce (1988), in a
prospective randomized study of pregnancies complicated by hypertension and/or growth restriction,
found that with Doppler examinations antenatal inpatient stay, rate of inductions, and even perinatal
mortality was signicantly reduced. Newnham et al.
(1991) by contrast found no clinical effect using Doppler ultrasound and no influence on perinatal morbidity or mortality. Tyrrell et al. (1990) compared the introduction of Doppler ultrasound and a biophysical
profile in high-risk pregnancies with selective use of
these techniques in a few cases. They found a significant reduction in neonatal depression and early morbidity with regular use, but no difference in perinatal
morbidity. Hofmeyr et al. (1991) compared Doppler
sonography of the umbilical a. with computer-aided
CTG analysis during primary monitoring of high-risk
pregnancies. They found a significant reduction in the
frequency of secondary cesarean sections in the Doppler group. The gross perinatal mortality was cut in
half, but this difference disappeared when cases with
Studies of Clinical Significance
lethal malformations were excluded (Giles and Bisits
1993).
By contrast Davis et al. (1992) even found a fourfold
increase in perinatal mortality in the Doppler group.
However, analysis of the clinical management reveled
that 85% (!) of the patients in this group had only a
single Doppler examination after the 22nd week, and
that in all cases with intrauterine fetal death the last
Doppler examination had been performed two to five
weeks previously. This error must be attributed to the
lack of standard management protocol,so that possible
abnormalities arising before the death of the fetus
were not detected. According to Trudinger et al. (1991),
serial, i. e., regular examinations, were not performed
in this series in 85 % of the subjects, but are essential
for prognostic significance, since placental insufficiency and associated changes in the Doppler findings
can be a progressive process.
Observational studies addressing the clinical significance of Doppler ultrasound lead to the expectation
that Doppler ultrasound can improve especially the
clinical management of IUGR. This applies not only to
the detection of genuinely growth-restricted fetuses,
but also to the avoidance of unnecessary diagnostic
measures in the presence of, for example, a constitutionally small fetus (Redman 1989). A
criterion for intervention either by intensive surveillance or elective delivery would appear to be the enddiastolic block in the umbilical a. because of its highly
significant association with perinatal morbidity and
mortality (Beattie et al. 1994, Pardi et al. 1993, Thornton and Lilford 1993).
These considerations were explored by Alström et al.
(1992) in a Scandinavian multicenter study of IUGR. In
contrast to the previously cited studies, this prospective randomized study included a complete standardized management protocol. It essentially mandated
the comparison of CTG with Doppler sonographyof the
umbilical a. during basic monitoring of the pregnancy
as well as primary cesarean section for Doppler sono-
graphic evidence of complete diastolic block after 32
weeks. The result showed significant reductions in inductions and secondary sections, while antenatal and
neonatal inpatient stays were shorter. On the other
hand, this study, too, found no difference in the total
section rate and the duration of the pregnancy. Hence
clinical use of Doppler ultrasound optimized obstetric
management without increasing prematurity or the
rate of cesarean sections.
Nienhuijs et al. (1990) similarly reported on the use
of Doppler ultrasound in the decision whether to continue ambulatory management or to admit for inpatient care in the management of growth restriction.
The incidence of inpatient care was significantly
smaller in the Doppler group than in the control group,
while the outcome of the pregnancy in general was
comparable between the groups. This result is con-
suitable
Doppler
sonant with the observation that pregnancies with
growth restriction, but normal Doppler finding, run an
essentially normal course.
Omtzigt et al. (1994) conducted a randomized controlled study to assess the clinical significance of Doppler sonography of the umbilical aa. in an unselected
clinic population. This study also included a standardized management protocol. This required that Doppler
ultrasound was introduced in the Doppler group only
when there was a risk to the fetus. The study found no
difference in clinical course or perinatal morbidity, but
there was a significant reduction in perinatal mortality, both raw and when lethal fetal malformations were
excluded. Neonatal mortality was not increased in this
study, i.e., the reduction in perinatal mortality was not
the result of a shift in fetal mortality into the neonatal
period.
Cumulative Metaanalysis
None of the cited studies in itself contains a sufficient
number of patients to demonstrate additional reductions in perinatal mortality, since this is already quite
low. From this point of view the reduction in perinatal
mortality found in the study of Omtzigt et al. (1994)
cited above can be viewed as the result of chance.
Using metaanalysis, however, it is possible to collect
the individual results of a number of different studies
that are similar in design and to evaluate them by
means of formal statistical methods (Collins et al. 1987,
Thompson and Pocock 1991). The cumulative results
can then be expressed as a typical odds ratio (OR) with
its associated confidence interval (95% CI). If the number 1 (no effect) lies outside this interval, a significant
effect of the intervention, with an error 쏝5 %, has been
demonstrated. Prospective randomized studies of interventions collected for metaanalysis must fulfill
other methodological and statistical quality criteria.
Giles and Bisits (1993) undertook a corresponding
evaluation of all studies that appeared in English
before 1991 and abstracted the essential results of six
studies in a metaanalysis (
method the typical OR for the effect of Doppler ultrasound on the raw perinatal mortality in high-risk pregnancies was 0.50 and the effect on the incidence of
stillbirth after exclusion of lethal malformations 0.54.
Hence integrating Doppler sonography of the umbilical
aa. into the clinical management of high-risk pregnancies leads to a halving of the mortality figures. It is
worth mentioning that this clinical advantage was
achieved without any increase in perinatal or maternal
morbidity.
A metaanalysis of just four of the six cited interventional studies (McParland and Pearce 1988, Newnham
et al. 1991, Omtzigt et al. 1994, Trudinger et al. 1987)
based on the Oxford and Cochrane databases for clinical studies in perinatal medicine also showed that the
Tables 17.2,17.3). By this
Advanced Topics
155
Diagnostic and Clinical Significance of Doppler Ultrasound in Obstetrics
Table 17.2 Effects of Doppler vs. conventional management
on perinatal mortality. Metaanalysis after Giles and Bisits
Lead Author Doppler Control OR 95 % CI
Trudinger (111) 1/133 5/167 0.32 (0.06−1.62)
McParland (78) 6/254 20/255 0.32 (0.15−0.71)
Omtzigt (86)* 16/809 28/789 0.56 (0.31−1.01)
Almström (2)
Hofmeyr (58) 4/438 8/459 0.53 (0.17−1.67)
Newnham (83) 9/254 9/251 0.99 (0.39−2.53)
Metaanalysis: 0.50 (0.34−0.73)
OR:Odds Ratio
CI: Confidence interval
*: Fir st published in 1990 as PhD thesis at the University of Utrecht
#
: Results were presented at the International Perinatal Doppler Society
meeting, 1991, Malmö, Sweden (J. Matern. Fetal Invest. 1: 127, 1991,
abstract)
3
Table 17.3 Effects of Doppler vs. conventional management
on the corrected
Bisits.
Lead Author Doppler Control OR 95 % CI
Trudinger (111) 0/133 1/167 0.17 (0.00−8.58)
McParland (78) 1/254 4/255 0.30 (0.05−1.74)
Omtzigt (86)* 10/809 22/789 0.45 (0.23−0.91)
Almström (2)
Hofmeyr (58) 1/438 1/459 1.05 (0.07−16.79)
Newnham (83) 9/254 9/251 0.99 (0.39−2.53)
Metaanalysis: 0.54 (0.32−0.89)
Cf. Table 17.2)
Table 17.4 Effect of Doppler vs. conventional management on
perinatal mortality of twin pregnancies. Historical comparisons.
Mortality Doppler
Perinatal:
− total 4 11 0.31 ⬍ 0.05
− corrected: 2 8 0.21 ⬍ 0.05
intrauterine: 1 6 0.14 ⬍ 0.05
n: Number of twin gestations with viable fetuses ex-
Mortality numbers: Number of individual affected fetuses or neonates
RR: Relative risk
#
0/214 3/212 0.13 (0.01−1.28)
$
stillbirth rate. Metaanalysis after Giles and
#
0/214 2/212 0.13 (0.01−2.14)
(n = 112)
amined 욷 28 weeks
Controls
(n = 95)
RR Chi2test,
P
clinical use of Doppler ultrasound in high-risk pregnancies halved the refined perinatal mortality (typical
OR: 0.51; 95% CI: 0.32−0.80).
Diastolic Reverse Flow
Management for (end-)diastolic reverse flow in the
umbilical a. has also been examined in a prospective
study, specifically in pregnancies between 23 and 29
weeks (Hadi et al. 1991). Admittedly, in this study the
Doppler results in both groups had to be open. In the
intervention group immediate cesarean section was
performed, while the control group was treated expectantly. In the intervention group 3 out of 10 newborns
died of immaturity, while all 10 fetuses in the control
group died in utero within 2 to 10 days. Further perinatological data could not be derived from the paper,
which was published only in abstract. In our own
patients with reverse flow in the umbilical a. we found
a median birthweight of only 600 g and a gestational
age of only 28 weeks. Thus, every other fetus did not
even attain a birthweight of 600 g and did not reach 28
weeks, but either died before that time in utero or had
to be delivered sooner by cesarean section b ecause of
an abnormal CTG (Gonser et al. 1993b). In view of these
extremely low birth weights, under the 1st percentile
(Roemer et al. 1990), and the immaturity, no standardized procedure can be offered at this time.
Multiple Pregnancy
A study that addresses clinical significance of Doppler
ultrasound in multiple pregnancy is that published by
Giles et al. (1988). Because of the low rate of twin pregnancies, a randomized study was not possible. Hence
the study compared the intervention group with the
chart review of a control group. The result was a significant reduction in both raw as well as refined perinatal
mortality (by a factor of 3 or 4!). This effect related
principally to a reduction in the incidence of in-
Table
trauterine fetal deaths (
dies there was no negative effect on gestational age or
the mode of delivery.
17.4) and as in other stu-
156
Conclusions
Numerous observational studies have demonstrated
that Doppler ultrasound provides an efficient mode of
monitoring high-risk pregnancies, especially when
there is a predisposition to hypertensivecomplications
of pregnancy or for IUGR. Growth-restricted fetuses
have a higher perinatal morbidity and mortality than
full-grown infants (Heinomen et al. 1985, Jones and
Roberton 1984, Low et al. 1975) and hence require in-
tensive perinatal monitoring. In this respect the Doppler procedure is not as suitable for a primary diagnosis of such retardation as for the identification of actual
nutritional and respiratory deficiencies in a growth restriction previously detected by ultrasound (Lowery et
al. 1990, Malcus et al. 1991, Maršál 1991). If a fetus has
been found to be small by biological measurements,
and the pregnancy is unremarkable with normal Dop-
Conclusions
pler findings, the prognosis over the remaining course
of the pregnancy is very favorable and ambulatory
monitoring appears to be adequate (Almström et al.
1992,Burke et al. 1992, Maršál and Persson 1988, Nienhuijs et al. 1990, Redman 1989, Rochelson et al. 1987b).
Pardi et al. (1993) suggested adding umbilical cord
puncture with blood gas analysis to optimize the management of IUGR with abnormal Doppler findings in
the umbilical a. However, the risk of inducing bradycardia by such a puncture is especially great in these
fetuses (in growth restriction: 15% to 18%; in end-diastolic block as much as 21%) (Weiner et al. 1991). Hence
such a procedure needs to be clarified by suitable controlled interventional studies (Soothill 1993a).
Compared to the number of observational studies
addressing diagnostic significance, there are considerably fewer interventional studies addressing clinical
significance. The intervention consisted of the integration of Doppler findings into clinical management, but
in most cases no standardized management protocol
was provided. In almost all interventional studies Doppler ultrasound had a positive effect on obstetric management, resulting in improved pregnancy outcome.
In two of the cited controlled interventional studies
the integration of Doppler ultrasound into obstetric
management resulted in the observation that perinatal
mortality was significantly reduced (McParland and
Pearce 1988, Omtzigt et al. 1994), even though these
studies were not designed to demonstrate this effect.
This fact limits the value of this result (Altman 1983). If,
for instance, a study is to show that the introduction of
a new procedure into obstetric management reduces
the perinatal mortality from, say, 5 to 2.5 per 1000, the
study group and the control group each must include
close to 10 000 patients for such a clinical study to have
a level of significance of 쏝 5% (α error 쏝 5 %) and a
powerofover80%(β error 쏝 20 %) (Lilford 1987 and
1989). An indirect solution of this dilemma is provided
by a cumulative metaanalysis of several individual,
correspondingly well-documented comparable studies, such as were registered in the Oxford database for
perinatal studies (Chalmers et al. 1986). In addition,
the number of cases required can be reduced by confining the study to high-risk pregnancies, since a significant reduction is more likely to be attained when
the initial mortality is higher. Adhering to these principles, Giles et al. conducted an exemplary metaanalysis of management studies published in England up to
and including 1991. The study proved that the perinatal mortality was cut in half in high-risk pregnancies
when Doppler ultrasound was used, without any negative effect on maternal and neonatal morbidity (Giles
and Bisits 1993). However, these results should undergo further critical review. Beyond that, with few exceptions, there are no concrete procedural guides for
the integration of Doppler ultrasound into obstetric
management. In this respect clear indications are imperative, not least because some reservations have
been expressed recently concerning the safety of the
acoustic intensity of pulsed Doppler instruments
(European Federation of Societies for Ultrasound in
Medicine and Biology [EFSUMB] 1992).
For the statistical reasons noted above a measurable
clinical usefulness of Doppler ultrasound can only be
expected with wide application and standardized procedures (De Bono et al. 1992, Thornton and Lilford
1993). Hence an examination that is to be used clinically must be simple to perform and robust. These requirements were best met by examinations of the
umbilical aa. (Maršál 1991). Controlled interventional
studies of the clinical significance of Doppler sonography of other fetal vessels, such as aorta, cerebral vessels, IVC, or umbilical v.’s, are still pending. Given the
differentiated insight into fetal pathophysiology these
would provide, an even more favorable influence on
clinical management might be expected. Women at
24−32 weeks of gestation might even benefit from
such studies, for in problem cases this is the time when
it is imperative to determine the diagnostic measures
and the clinical management best suited to find the
optimal time for delivery between increased intrauterine risk and severe immaturity (Thornton and
Lilford 1993).
The perinatal prognosis in high-risk pregnancies can
at best be improvedto the extentthat the development
of pathology can still be influenced at the point in time
when the findings are obtained. Hence a differential
diagnosis in high-risk pregnancies should be made at a
point in time when they are still accessible to treatment. An example for such an approach is the selection
by Doppler ultrasound of those pregnant women who
could benefit from the administration of low-dose
aspirin to reduce the risk of hypertensive complications of pregnancy (McParland et al. 1990). An effective
differential diagnosis is important, for indeed the Collaborative Low-dose Aspirin Study in Pregnancy
(CLASP study) led to a significant reduction in the
frequency of preeclampsia and halving of the perinatal
mortality under 32 weeks (5.3 % vs. 10.6%) only when a
daily dose of 60 mg aspirin was targeted to the prophylaxis of preeclampsia. In contrast, administering
aspirin in all high-risk pregnancies without such diagnosis proved to be useless (CLASP 1994).
Advanced Topics
157
Diagnostic and Clinical Significance of Doppler Ultrasound in Obstetrics
Summary
3
Diagnostic significance is measured by the reliability
with which Doppler parameters in pregnancy are associated or correlated with outcome parameters. The
measure of clinical signif icance, on the other hand, is
how effective the clinical introduction of the procedure is in improving the course and outcome of the
pregnancy. Therefore, the adequate procedure to
measure diagnostic significance is the observational
study, while the ideal procedure to measure clinical
significance is the prospective, randomized management or interventional study.
The literature contains numerous observational studies addressing diagnostic significance. These show
that there is a significant link between abnormal Doppler findings and the consecutive obstetric pathologies: growth restriction, prematurity, acidosis by cordocentesis, abnormal prenatal CTG, neonatal depression and acidosis, and neonatal intensive care.
Such findings, however, should in no way lead to the
conclusion that the information so obtained can improve pregnancy outcome. That question can only be
answered by suitable clinical management studies. In
the prospective randomized studies currently available, a positive clinical effect was demonstrated in highrisk pregnancies. These studies showed that compared
to the control group the Doppler group resulted in a reduction in prenatal and neonatal inpatient stays, induction rate, and frequency of secondary cesarean section. At the same time there was no difference in the
duration of gestation or the total section rate.
However, none of the studies contained a sufficient
number of patients to substantiate a further reduction
in the already very low perinatal mortality with any assurance. Nevertheless, using cumulative metaanalysis,
the discrete effects of individual well-documented studies with similar design can be collected and evaluated. Such studies show that the introduction of Doppler ultrasound into the clinical management of highrisk pregnancies leads to a halving of the raw as well as
the refined mortality. It should be mentioned that this
effect is achieved without an increase in neonatal or
maternal morbidity and without a shift of fetal mortality into the neonatal period.
158
18 Doppler Sonography of the Fetal Venous Circulation
It is known from numerous animal studies on sheep
and primate fetuses that the venous circulation, consisting of umbilical v. (UV), ductus venosus (DV), portal
v.’s, hepatic v.’s, inferior vena cava (IVC), and the right
atrium with the foramen ovale, reflects the central
venous pressure and cardiac function. It is also known
to play an important role in the regulation of the fetal
circulation.
Blood flow in the UV was measured even before the
application of Doppler ultrasound in obstetrics in 1980,
especially volume flow to monitor fetuses with rhesus
incompatibility (Eik-Nes et al. 1980). Subsequent studies concentrated increasingly on the arterial blood
vessels of the fetus and on the uterus. Only after the
advent of color Doppler ultrasound did it become
Anatomy
Oxygenated blood from the placenta reaches the body
of the fetus through the venous system. The UV enters
the fetal abdomen and first runs acutely backward and
upward, then divides in the liver into the portal v. (PV)
and the DV. From this point, known as the portal sinus,
the left PV runs to the right, while the DV runs to the
left and in a dorsocranial direction, as it were the con-
18.1).
tinuation of the UV (
Fig.
possible to record the rest of the venous circulation
with its narrower vessels and in part very slow blood
flow velocities, and to display the anatomical peculiarities of the humans fetus.
Since the beginning of the last decade studies of
blood flow in the IVC and the DV were primarily
selected for study, but flow in the hepatic v.’s and
around the foramen ovale was also studied (Reed et al.
1990, Huisman et al. 1991 and 1992b, Kiserud et al.
1992a, Rizzo et al. 1992, Hecher et al. 1994).
More recently Doppler studies designed to extend
our understanding of the fetal circulation in health and
disease have also included the conditions of flow in the
superior vena cava, the portal v.’s, and the pulmonary
v.’s.
The DV is a trumpet-shaped connection between the
UV and the proximal part of the IVC. It is only 2 mm
wide at its origin.
The left PV anastomoses with the branches of the
right PV, and both supply placental blood to the right
lobe of the liver, which receives 80% of the hepatic
circulation. The venous drainage takes place through
the wide-branching right hepatic v. (RHV) (
Fig. 18.2),
Advanced Topics
Fig. 18.1 Umbilical vein (UV) and ductus venosus (DV) displayed in a cross section of the fetal abdomen. (LHV = left hepatic vein)
Fig. 18.2 Right hepatic vein (RHV) displayed in a cross section
of the fetal abdomen.
159
Doppler Sonography of the Fetal Venous Circulation
Fig. 18.3 Longitudinal section of the fetal abdomen with display of the junction of the precordial v.’s at the upper portion of
the inferior vena cava (IVC). (UV = umbilical vein, DV = ductus
venosus, HV = hepatic vein)
3
Physiology
the main branch of which is the most proximal of the
precordial v.’s to drain into the IVC. The UV itself supplies the left lobe of the liver directly with blood which
flows into the IVC through the left and middle hepatic
v.’s (LHV and MHV).
The proximal part of the IVC, the DV, and the three
hepatic v.’s together form a space situated immediately
under the diaphragm before the right atrium, as Huisman et al. (1992a) were able to demonstrate in their
anatomical studies. This should be taken into account
when the precordial v.’s are examined by Doppler ultrasound, in order to avoid overlapping signals
ig.
F
18.3).
(
The DV plays an essential role in the regulation of the
fetal circulation. It is one of three shunts and links the
UV with the IVC. About 50−60 % of the oxygenated
blood passes through the DV directly to the fetal heart.
The constriction of the lumen of the DV to about a third
of the width of the UV and the differences in pressure
and resistance in the hepatic and cardiac circulations
increase the blood flow velocity from 20 cm/s in the UV
to 60−80 cm/s in the DV. Nervous and hormonal influences as well as a sphincter muscle have been suspected of taking part in the regulation of blood flow
through the DV, but anatomical correlates for such
mechanisms are lacking.
The remaining 40−50 % of the blood in the UVs first
pass through the PVs into the liver, and then through
the hepatic v.’s into the IVC. The oxygen saturation in
the UV and the DV is about 80−85 %, while in the distal
IVC and the RHV it is only 35 % or 50 %.
Animal experiments using microspheres carrying
radionuclides show two streams of blood, which do
not mix, flowing from the proximal IVC to the heart.
Kiserud et al. (1992b) used color Doppler ultrasound to
show that in the human fetus there are also two crossing inflows to the heart in this area, the left path leading from the DV to the foramen ovale, the right path
from the IVC to the right atrium.
The Left Path from the Ductus Venosus to the
Foramen Ovale
Well-oxygenated blood from the UV passes through
the DV into the left dorsal part of the proximal IVC. The
position of the dividing crest of the foramen ovale and
the eustachian valve directs this blood flow directly
through the foramen ovale into the left atrium. By this
route blood rapidly reaches the vital organs, such as
brain, heart, and adrenals.
The LHV and MHV, with an oxygen saturation of 70−
18.4).
75%, also enter this path (
Fig.
The Right Path from the Inferior Vena Cava to the Right Atrium
160
Fig. 18.4 The left path of DV−foramen ovale. (UV = umbilical
vein, DV = ductus venosus, MHV = middle hepatic vein, LA = left
atrium)
The less well oxygenated blood from the lower body
and the RHV flows from the anterior right-hand side of
the proximal IVC primarily into the right atrium and
through the tricuspid valve into the right ventricle.
From here it passes through the pulmonary circulation
and from there chiefly into the descending thoracic
aorta through the ductus arteriosus (
These blood streams effectively do not mix and ensure that the oxygenated blood from the placenta pref-
Fig. 18.5).
Ultrasound Display and Doppler Sonography of the Venous System
erentially supplies the small left fetal circulation, while
the poorly oxygenated blood from the fetal body returns to the placenta by way of the right heart, the ductus arteriosus, and the aorta.
If the resistance in the placental be d increases, with
a rise in the cardiac afterload, and/or a reduction in the
venous return, blood flow through the DV may increase up to 70 %, partly by an increase in hepatic resistance, partly by dilatation of the cerebral vessels.
This shift ensures an adequate venous return to the
fetal heart, and a good oxygen supply to the vital or-
gans, i. e., the brain, heart, and adrenals. In addition,
changes in the lumen of the DV modify its blood flow.
This may be attributed to nervous factors or some kind
of sphincter, and may become manifest by wide fluctuations occurring in the flow curves in the DV within a
brief examination period.
Fig. 18.5 The right path of IVC−right atrium. (IVC = inferior
vena cava, RA = right atrium)
Ultrasound Display and Doppler Sonography of the Venous System
Depending on the position of the fetus, a median longitudinal cut or a somewhat obliquely set cross section
have been established as the best way to display the
fetal v.’s. For the examination of the IVC a lateral longitudinal or a coronal cut is the best choice.
The UV should be focused at its entrance into the
fetal abdomen and the blood flow measured by pulsed
Doppler. Normally the blood flow in the UV will appear
monophasic and band-like, with a peak velocity of
about 20 cm/s.
The DV should be examined at its origin from the UV,
the hepatic v.’s about 5 mm proximal to their junction
with the IVC, and the IVC between the junction of the
DV and the renal v.’s. This will avoid interference from
18.6,18.7).
neighboring vessels (
As in the Doppler examination of the arteries, the
fetus should not be breathing or moving. The insonation angle should be less than 30°, and this is easily accomplished when focusing the DV, UV, and RHV. The
IVC, on the other hand, can usually only be focused at
an angle of 50−60°.
In contrast to the UV (
in the veins closer to the heart is pulsatile. The forward
flow toward the heart has two peaks. The first peak occurs during ventricular systole (S = filling of the atria)
followed by a decline in blood flow toward the end of
systole (ES = maximal filling of the atria). The second
peak occurs in early diastole (D) during passive filling
of the ventricles when the atrioventricular (AV) valves
open. Reverse flow into the IVC and the hepatic v.’s occurs during active atrial contraction in late diastole (A)
18.9).
Fig.
(
Peak blood flow velocity is attained in systole and
reaches about 40 cm/s in the IVC and 20 cm/s in the he-
Figs.
Fig. 18.8), the blood flow curve
Fig. 18.6 Point of measurement and blood flow curve of the
DV.
Fig. 18.7 Point of measurement and blood flow curve of the
IVC.
Advanced Topics
161
Doppler Sonography of the Fetal Venous Circulation
Fig. 18.8 Blood flow pattern of the DV and the UV. Fig. 18.9 Characteristic blood flow curve of the RHV.
162
3
Fig. 18.10 Characteristic blood flow curve of the DV.
Results of the Doppler Studies
In longitudinal Doppler studies of the precordial v.’s in
normal pregnancies there is a continuous increase in
forward flow to the heart and a decrease in return flow
into the veins as the pregnancy progresses (Huisman et
al. 1991 and 1992b, Kiserud et al. 1992a, Rizzo et al.
1992, Hofstaetter et al. 1996).
This reflects better cardiac filling by increasing atrial
relaxation and improved cardiac emptying by a reduction in flow resistance in the placental bed as the pregnancy progresses.
Beyond that, if cardiac function is impaired, venous
blood flow changes by a reduction in venous inflow, increase in venous inflow, or by a reduction in cardiac
stroke volume due to an increased postcardiac resistance. The latter may be due to increasingly severe
patic v.’s. Blood flow in the DV normally continues forward, because of its higher blood flow velocity that
Fig.
may peak at 60−80 cm /s (
Besides peak velocities in systole (S), early diastole
(D), and during atrial contraction (A), as well as average maximal velocity (TAMX) a number of indices are
calculated for Doppler sonography of the fetal v.’s.
Those applied most commonly are the S/A ratio, the
pulsatility index for veins (PIV = S−A/TAMX), the peak
velocity index for veins (PVIV = S−A/D), the DV index
after De Vore (S−A/S), and in the case of the IVC and the
hepatic v.’s the percent reverse flow (RF in % = time ×
TAMX of reverse flow during atrial contraction in late
diastole : time × TAMX of forward flow during ventricular systole and early diastole) (Reed et al. 1990, Huisman et al. 1991 and 1992b, Kiserud et al. 1992a, Rizzo
et al. 1992, Hecher et al. 1994, De Vore and Horenstein
1993).
placental insufficiency (absent or reversed diastolic
[ARED] flow), to tachyarrhythmias, or myocardial
failure.
The flow pattern in the UV is monophasic and in a
normal case has a maximal flow velocity of 20 cm/s
and a volume flow of 120 mL/kg/min in early pregnancy and 90 mL/kg/min at term.
A pulsatile pattern in the UV is only physiological
until the 15th week of gestation. After that pulsations
in the umbilical cord are always pathological. Simple
pulsations in the UV during ventricular systole may be
found when the umbilical cord is compressed
ig.
F
18.11).
(
Pulsations in the intra-abdominal portion of the UV
during atrial contraction in late diastole (Fig. 18.12)are
18.10).
a reflection of elevated intra-arterial pressure. This
may result from increased cardiac preload, such as hypervolemia due, for example, to hydrops fetalis, in the
acceptor twin in a feto−fetal transfusion syndrome
(FFTS), or a cardiac malformation with reduced cardiac
inflow, or it may occur when raised resistance in the
placental bed increases the cardiac afterload. Back flow
into the veins (so-called A blood flow) in these cases
increases in the IVC and the hepatic v.’s, while decreas-
Fig.
ing in the DV (
18.13).
As the resistance in the placental bed increases and
as a result the fetal circulation becomes increasingly
centralized, the afterload continues to increase. If the
coronary circulation then is no longer adequate, pressure at the end of ventricular systole increases, leading
to double pulsations in the UV (Fig. 18.14). This is an
ominous sign, signifying the breakdown of circulatory
compensation in the fetus due to myocardial insufficiency. The raised right atrial pressure passes through
the DV directly into the UV. Mostly there is reverse flow
in the DV during atrial contraction (
Fig .18.15). Double
pulsations in the UV and reverse flow through the DV
are associated with a fetal mortality of 70% and a morbidity of about 90%.
In a study of fetuses with hydropsfetalis Gudmundsson et al. (1991) were able to show that pulsations in
the umbilical cord are a sign of impaired cardiac function and are associated with a poor pregnancy outcome. If, on the other hand, hydrops fetalis was due to
a viral infection, pulsations were absent and the fetuses survived.
The raised intra-atrial pressure leads to an increase
in reverse flow in the IVC and the hepatic v.’s during
atrial contraction (A blood flow). There is a decrease in
A blood flow in the DV. The SA ratio and S−A/S ratio, the
PIV, the PVIV, and the RF rise correspondingly in %
Figs. 18.16,18.17) (Rizzo et al. 1992, Kiserud et al.
(
1994, Rizzo et al. 1994, Hecher et al. 1995, Gudmundsson et al. 1996).
Results of the Doppler Studies
Fig. 18.11 UV pulsation due to compression.
Advanced Topics
Fig. 18.12 Single UV pulsations during atrial contraction in late
diastole.
Fig. 18.13 Abnormal blood flow in the DV with reduced A
blood flow.
163
Fig. 18.14 Double pulsations in the UV.