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Physiology of Doppler Flow in Maternal Vessels during Pregnancy
without an increased difference between the two sides), we interpreted this as a severe form of abnormal uterine perfusion.
These groups (III, V,and VI) had severefetal circulatory changes
that affected all the fetal vessels, suggesting that the presence
of two or three abnormal perfusion parametersleads to serious
fetal compromise
7
. For this reason, Doppler velocimetry of
both uterine arteries is recommended for the clinical assessment of uterine perfusion.
Postsystolic notch. A postsystolic notch in uteroplacental
waveforms during the second half of pregnancy indicates an
abnormal pulse-wave reflection in the spiral arteries—presumably a result of deficient trophoblastic invasion during
placentation. The presence of a postsystolic notch is the Doppler sign of preeclampsia
3
and has a very strong association with
intrauterine growth retardation.The notch should no longer be
detectable after 24 weeks’ gestation; otherwise there is a 70 %
likelihood of a pregnancy complication with hypertension
Uterine Perfusion on Medication or after Uterine Manipulation
13
Mechanisms of action of intravenous beta-mimetics. The increased perfusion rate of the gravid uterus in response to intravenously administered beta-mimetics is based on two
mechanisms: an increase in cardiac output and a lowering of
peripheral vascular resistance. Since we also observed a fall in
the pulsatility index, it is reasonable to assume that the more
important mechanism is peripheral vasodilation. The calculated pulsatility index is less affected than the S/D ratio by an
increased diastolic blood flow velocity caused by the increase
in cardiac output.
No effect of amniocentesis, cervical cerclage, or oral beta-mimetics. In our study population, which was homogeneous for
gestational age, we found that amniocentesis, cervical cerclage, and orally administered beta-mimetics produced no
change in uterine perfusion that was measurable by vaginal
sonography. The intravenous administration of beta-mimetics
led to a fall in the S/D ratio and pulsatility index.
Our findings confirm the clinical experience that none of
the foregoing procedures hampers blood flow to the pregnant
uterus and that the intravenous administration of beta-mimetics even appears to improve it.
It is interesting to note that nifedipine administration pro-
duces similar
results
sponse to indomethacin
29
, but this effect has not been seen in re-
therapy
21
.
Doppler Flowmetry of Maternal Vessels as a Screening Test?
The Doppler flowmetry of maternal blood vessels is an important step in evaluating the blood flow of the fetomaternal
11, 3 2
unit
trimester, the transvaginal pulsed Doppler velocimetry of both
uterine arteries can also be recommended as a screening test at
the end of the second trimester. Placentation is already
complete by this time, so that the physiological processes of
trophoblastic invasion will not produce false-positive findings
(difference between the sides).
14
.
Sensitivity for lateral hypertension. When both uterine arteries
are examined and the resistance indices are calculated, Doppler velocimetry of the uterine arteries can be done as early as
the 22nd week of gestation to screen for pregnancy complications. In the study by Valensise et al.
sensitivity of 50% for predicting later pregnancy-induced hypertension, 88% for preeclampsia, and 100% for intrauterine
growth retardation.
Negative predictive value. Abnormal uterine artery waveforms
can have clinical implications when detected as early as the
24th week of gestation. The negative predictive value of this
method is impressive: with a normal finding, there is a 96 %
likelihood that a pregnancy complication will not occur
sufficient in these cases to schedule follow-up examinations at
about four-week intervals. It should be emphasized, however,
that not all pregnancy complications can be predicted and diagnosed by Doppler flowmetry. It has been shown that this
method is most rewarding in cases of pregnancy-induced hypertension or intrauterine growth retardation, and therefore
the test should be performed in patients who are considered
from their history to be at risk.
False-positive results. On the other hand, there is a possibility
of false-positive test results, and the measurements cannot always be interpreted with complete certainty. As a result,
uterine artery velocimetry cannot presently be recommended
as a general screening test for all pregnancies
. Besides its use for risk assessment in the first
39
, this screening test had a
33
.Itis
2, 17
.
122
Summary
Doppler velocimetry of maternal vessels is one tool that is used
for evaluating the perfusion of the fetomaternal unit. The most
rewarding vessels are those that are directly or indirectly responsible for sustaining the pregnancy. Abnormalities in the
waveforms of major uterine vessels show a strong correlation
with the presence or subsequent development of fetal growth
retardation and preeclampsia. Flowmetry of the arcuate arteries can sometimes lead to false results in patients with extensive placental infarcts and in smokers because the examination
is confined to a circumscribed, terminal portion of the vascular
bed.
Doppler velocimetry in a normal early pregnancy demonstrates high systolic and low diastolic flow velocities combined
with a high S/D ratio and a high pulsatility index. The diastolic
flow velocity increases with advancing gestation, leading to a
decline in the S/D ratio and pulsatility index.
References
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38 Trudinger BJ, Giles WB, Cook CM: Uteroplacental blood flow velocity-
time waveforms in normal and complicated pregnancy. Brit. J. Obstet.
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C: Doppler velocimetry of the uterine artery as a screening test for gestational hypertension. Ultrasound Obstet. Gynecol. 3 (1993) 18–22
40 Wladimiroff JW, Tonge HM, Stewart PA: Doppler ultrasound of cere-
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Obstetric Ultrasound
123
Color Doppler Sonography of the Uterine Arteries in
14
Early Pregnancy to Screen for Preeclampsia and
Uteroplacental Insufficiency
A. Funk
Applications of Color Doppler Sonography during Pregnancy
Placental insufficiency and preeclampsia in the third trimester.
Doppler sonography of the uterofetoplacental unit in the third
trimester is part of the standard diagnostic workup of patients
with suspected placental insufficiency and preeclampsia. At
this late stage of gestation, however, it is possible only to confirm the presence of a chronic perfusion def icit. The Doppler
findings, along with B-mode findings and biophysical and biochemical tests, are helpful in assessing the degree of fetal compromise and directing clinical management.
14
Early detection of decreased uterine perfusion. The efforts of
modern me dicine are also aimed at early detection, clinical intervention, and prevention, and these goals have prompted the
use of transvaginal ultrasound scanning to assess blood flow
early in the pregnancy.
Changes in the spiral arteries. The central question is whether
Doppler sonography is able to confirm the normal development of blood flow and also detect decreased blood flow
during the first half of pregnancy. Another key issue is whether
Doppler evidence of decreased uterine perfusion actually
correlates with the development of pregnancy-induced hypertension (PIH) and intrauterine growth retardation.
Normally a massive increase of blood flow occurs during
the first half of pregnancy, and this requires a morphological
transformation of the spiral arteries as described by Brosens et
3
al.
. Trophoblastic cells invade and erode the musculoelastic
media of the spiral arteries, transforming the vessels into large,
saclike tubes with a funnel-like expansion at their junction
with the intervillous space. These changes take place between
the 14th and 20th weeks of menstrual age and are completed
no later than the 24th week, even when maturation is delayed.
The calibers of the spiral arteries are increased by a factor of 30,
the arcuate arteries by a factor of 10, and the uterine arteries by
a factor of 1.5–3
Blood circulation in the intervillous space. The blood flow
changes that occur during the first trimester are more difficult
to classify. Hustin and Shaaps
logical, and morphological studies showing that intervillous
blood circulation does not occur before the 12thweek of gestation. This led them to conclude that there is no contact between
the chorionic villi and maternal blood during the first trimester
andthat theembr yo andplacenta areindependent ofthe maternalenvironment. Theydistinguished betweena periodin which
implantation, organogenesis, and placentation occur and a second period that begins with active maternalblood flow through
the intervillous space toward the end of the first trimester.
It is reasonable to conclude that uterine blood flow in the
first trimester is controlled in part by the rising estrogen levels
in the maternal serum. This can be inferred from the fact that
cyclic changes in uterine blood flow correlate with the
estradiol level
in muscle cells of the uterine arteries
have shown dilatation of the terminal segments of the uterine
vessels prior to trophoblast invasion
2
.
7
performed hysteroscopic,radio-
4, 12
, that estrogen receptors have been identified
9
, and that animal studies
10
.
124
Technique of Transvaginal Doppler Sonography
Transducer placement. With the patient in the lithotomy posi-
tion, the ultrasound probe, sheathed in a condom and smeared
with contact gel, is inserted into the vagina until it is in contact
with the anterior fornix (anteflexed uterus) or posterior fornix
(retroflexed uterus). An initial survey is carried out, and the
probe is positioned in the lateral fornix so that it is in direct
contact with the uterine attachment of the parametrium
through the vaginal wall. The proximity to the target organs
makes it possible to use transducer frequencies of 5 MHz or
higher, which are excellent for blood flow studies.
Vascular anatomy. After arising from the internal iliac artery,
each uterine artery, surrounded by the uterine veins, curves
over the ureter about 2 cm from the cervix and reaches the
uterus at the level of the isthmus. There it divides into a descending cervical branch and an ascending branch. The latter
branch ascends tortuously along the side of the uterus and
anastomoses with the ovarian artery via the tubal branch. The
best sites for recording Doppler signals are the main trunk of
the uterine artery and the origin of the ascending branch. Both
vessels can be clearly identified in those areas and can be
scanned at an optimum beam–vessel angle.
Advantages of transvaginal scanning. According to our studies,
the transvaginal approach has several major advantages over
transabdominal scanning, especially in early pregnancy examinations
5
:
Normal Development of Uterine Artery Doppler Spectra
➤
Accurate overall assessment of uterine perfusion
➤
Greater pulsatility of blood flow, allowing better recognition
of impedance criteria in the Doppler scan
➤
Smaller range of error owing to a more favorable beam–vessel angle
Normal Development of Uterine Artery Doppler Spectra
The Doppler spectra of the uterine arteries display characteristic changes from early pregnancy until the conclusion of trophoblastic invasion in midpregnancy (Fig. 14.
Doppler spectra in early pregnancy. At the start of pregnancy,
the Doppler spectra of the uterine arteries do not differ from
those recorded in the periovulatory period. Highly variable
patterns can occur. The spectra typically have a sharp systolic
upstroke and downstroke with a sharp, narrow systolic peak
and a low maximum frequency shift. A variable notch may appear in the systolic downstroke. The diastolic phase of the cardiac cycle consistently shows a very low frequency shift whose
1).
pattern changes more characteristically with advancing gestation than the systolic peak. During the first trimester the sharp
systolic downslope typically ends in an early diastolic notch,
which may convert to reverse flow during the initial weeks.
The postsystolic notch is followed by a diastolic peak that
shows the highest velocities in the diastolic part of the cardiac
cycle during the first trimester. The end-diastolic frequency
shift is low in the first trimester, and absent or reverse flow is
seen in rare cases. These normal features during early pregnancy are useful for the visual interpretation of Doppler
waveforms in cases where abnormalities develop later in the
pregnancy.
Changes after the first trimester. The characteristic changes
past the first trimester are a continued increase in the systolic
maxima with broadening of the systolic peak and an increasingly high diastolic frequency shift, with disappearance of the
early diastolicnotch. The increase in flow velocities is relatively
greater at end diastole than in systole. The angle between the
systolic downstroke and the maximum diastolic frequencies
becomes greater, and there is an overall flattening of the spectral waveform. Generally this development is completed in the
20th week of gestation or by the 24th week at the latest.
Obstetric Ultrasound
Fig. 14.1 Comparison of uterine Doppler spectra recorded during
the first half of pregnancy.The maximum frequency shift in each spectrum can be read on the adjacent scale. Arrows = systolic notch;
N = early diastolic notch.
Normal Values in Early Pregnancy
Progression of values from weeks 4 to 24. In a prospective
longitudinal study, the progression of normal values for Doppler ultrasound parameters was documented from the 4th to
24th weeks of menstrual age. Of 257 pregnancies examined, 79
met the criteria for inclusion in the study (confirmed dates at
examination, no significant uterine anomalies, uncomplicated
singleton pregnancy, term delivery of a healthy eutrophic infant) based on a retrospective postpartum review. A maximum
of 117 individual examinations of the uterine vessels could be
evaluated. In addition to the standard indices, the early diastolic notch frequency and maximum diastolic frequency were
also determined. The latter quantities were used to calculate
an index, the notch/peak (N/P) ratio, which characterizes the
presence or absence of an early diastolic notch in the spectral
waveform. The data from both uterine arteries were used in
calculating all the indices. The following instruments were
available for the study: Combison 320–5 combined with the D
300 Doppler unit (Kretztechnik, 5 MHz vaginal probe) and the
128 XP/10 color Doppler unit (Acuson Corp., 5 MHz vaginal
probe). SAS software from the Department of Medical Information and Biometry of Aachen Medical College was used for
statistical analysis. The progressions of normal values for the
S/D ratio, resistance index (RI), pulsatility index (PI), and N/P
ratio are summarized in Table 14.
1.
125
Screen for Preeclampsia and Uteroplacental Insufficiency
Table 14.1 Normal values of uterine artery Doppler indices from the 4th to 24th weeks menstrual age
Weeks n Mean SD P5 P10 P50 P90 P95
S/D ratio (n = 100)
4– 6 14 12.18 8.14 4.87 6.44 10.26 15.45 38.50
7– 9 13 9.54 3.68 4.92 5.53 7.92 13.90 16.77
10–12 8 5.97 4.62 2.86 2.86 4.04 16.75 16.75
13–15 16 3.89 1.59 2.15 2.50 3.47 7.08 7.20
16–18 24 *2.87 1.32 1.97 2.06 2.43 3.70 6.14
19–21 13 2.38 0.37 1.79 1.82 2.37 2.80 2.83
22–24 12 2.14 0.21 1.64 1.99 2.12 2.39 2.45
RI (n = 104)
4– 6 15 0.89 0.04 0.79 0.84 0.89 0.95 1.00
7– 9 13 *0.87 0.04 0.79 0.80 0.86 0.93 0.93
10–12 8 0.76 0.09 0.65 0.65 0.74 0.93 0.93
13–15 16 0.69 0.07 0.56 0.59 0.70 0.81 0.81
16–18 26 *0.61 0.08 0.49 0.51 0.60 0.72 0.75
19–21 14 0.56 0.06 0.44 0.45 0.56 0.63 0.64
22–24 12 0.52 0.05 0.39 0.49 0.53 0.57 0.58
14
PI (n = 102)
4– 6 15 3.32 0.78 1.85 2.36 3.39 4.37 4.80
7– 9 13 2.85 1.07 0.87 1.94 2.53 4.52 4.76
10–12 8 2.12 0.92 1.17 1.17 1.93 3.93 3.93
13–15 16 1.86 0.50 0.85 1.02 2.04 2.29 2.59
16–18 25 *1.25 0.61 0.73 0.79 1.09 1.94 2.93
19–21 13 1.06 0.24 0.66 0.77 1.02 1.44 1.52
22–24 12 0.87 0.23 0.52 0.72 0.82 0.99 1.49
N/P-Ratio (n = 99)
4– 6 15 0.595 0.18 0.10 0.44 0.67 0.74 0.80
7– 9 13 0.628 0.17 0.30 0.41 0.67 0.80 0.85
10–12 8 0.871 0.08 0.71 0.71 0.89 0.99 0.99
13–15 14 0.924 0.10 0.76 0.78 0.94 1.07 1.07
16–18 26 1.03 0.15 0.69 0.86 1.06 1.18 1.22
19–21 12 1.05 0.08 0.91 0.96 1.05 1.15 1.16
22–24 11 1.07 0.07 0.95 0.98 1.11 1.14 1.15
* Significant difference relative to previous value
Early Doppler Examination of Uteroplacental Blood Flow in Abnormal Pregnancy
126
Patients
Inclusion and exclusion criteria. This series consists of 25 preg-
nancies that were examined by transvaginal Doppler sonography
before the 25th week of gestation and had an abnormal course or
outcome. Inclusion criteria were confirmed dates at the time of the
examination, a singleton pregnancy, the development of PIH (dias-
tolic blood pressure ⬎90 mmHg in multiple readings) with or
without proteinuria (⬎300 mg/day), perinatal asphyxia based on
histologically confirmed placental insufficiency, and the delivery of
a growth-retarded infant (⬍10th weight percentile after Hohenauer). Pregnancies with premature delivery, fetal and/or chromosome anomalies, and early pregnancy loss ⱕ 16 weeks were excluded from the study.
Analysis. The methodology and statistical tools were the same as
described above. Statistical significance measured by the 10th and
90th quantiles was determined with the independent t-test with a
significance level of
values were of limited validity because of the high prevalence in the
selected at-risk population.
α = 0.05. The positive and negative predictive
Early Doppler Examination of Uteroplacental Blood Flow in Abnormal Pregnancy
Results
Maternal parameters such as age and number of pregnancies and
deliveries did not differ from those in the normal group. Significant
differences were seen mainly in the length of pregnancy (x =31.8
weeks, SD = 8.0 weeks), birthweight (x = 2009 g, SD = 1285 g), and
in the one- and five-minute Apgar scores.
Doppler parameters. None of the Doppler parameters showed significant dif ferences from a normal pregnancy during the first
trimester. Table 14.2 shows the data on specificity, sensitivity, and
predictive values from weeks 13–15 to weeks 22–24.It is not until
week 16, and thus after the end of the first trimester, that individual
values for the S/D ratio, RI, and PI exceeded the 90th quantile or individual values for the N/P ratio fell below the 10th quantile for a
normal pregnancy.
PI. With advancing gestation, the Doppler findings increasingly re-
flected the delayed maturation of uterine perfusion. The PI pro-
vided the best discrimination: 4 of 9 cases in weeks 16–18, 5 of 7
cases in weeks 19–21, and all 8 cases in weeks 22–24 were above
the 90th percentile. Starting in week 19, the PI showed a sensitivity
of 87% and a specificity of 92%. The results for the S/D ratio and RI
were slightly lower.
N/P ratio. The N/P ratio, which expresses whether an early diastolic
notch is present, had a mean value ⬎1 starting in weeks 16–18 of
uncomplicated pregnancies. This parameter also showed increasing sensitivity after 16 weeks. Reaching 83 % by week 19 (n = 15), the
sensitivity of the N/P ratio was slightly lower than that of the standard Doppler indices.
Discussion
Opening of the spiral arteries. The visible waveform changes in
the uterine vessels, like the progression of the calculated indices, reflect the morphological processes in the terminal
vascular bed that are causing progressive dilatation of the spiral arteries. The variability of the frequency spectra seen during
the initial weeks may be attributable to differences in endovascular trophoblastic invasion and to individual factors
such as hormone levels and vascular calibers
show that it is not possible to distinguish between normal and
delayed or impaired perfusion during the first trimester. The
significant difference from weeks 13–15 to weeks 16–18 indicates that a disproportionately large decrease in vascular resistance occurs at the start of the second trimester. This may
reflect increasing uterine perfusion after the spiral arteries
have opened toward the intervillous space
Secondary trophoblastic invasion. Secondary trophoblastic in-
vasion is crucial for the development of uteroplacental blood
flow. The characteristic Doppler changes that occur during this
period are a rise in maximum flow velocities throughout the
cardiac cycle with a relative predominance in diastole and a
flattening or disappearance of the early diastolic notch (in
weeks 16–18 on average). A key observation is that there was
no case in which uterine blood flowdeveloped normally at first
and then became abnormal secondarily. At the same time, it
was common to find a late onset of normal blood flow with disappearance of the early diastolic notch by the 24th week of ges-
7
.
6
. Our results
Table 14.2 Accuracy of uterine artery Doppler examination from the
13th to 24th weeks of menstrual age in predicting the development of
pregnancy-induced hypertension or uteroplacental insufficiency
Weeks n Sensi-
tivity
(%)
S/D ratio
13–15 2 0 93 0 88
16–18 8 37.5 92 60 92
19–21 6 67 92 80 86
22–24 7 100 92 87.5 100
ⱖ 19 13 85 92 85 92
RI
13–15 2 50 93 50 93
16–18 8 25 92 50 79
19–21 6 33 92 33 67
22–24 7 100 92 87 100
ⱖ 19 13 69 92 82 85
PI
13–15 2 0 94 0 88
16–18 9 44.5 92 67 83
19–21 7 71.5 93 83 87
22–24 8 100 92 89 100
ⱖ 19 15 87 92 87 92
N/P ratio
13–15 2 50 93 50 93
16–18 9 44.5 92 67 83
19–21 7 57 92 80 78
22–24 8 87.5 91 87.5 91
ⱖ 19 15 83 91 84 85
tation. Aristidou et al.
1
Speci-
ficity
(%)
Positive
predictive
value (%)
Negative
predictive
value (%)
attribute this to a delayed but otherwise
normal process of trophoblastic invasion and placental maturation.
Correlation of Doppler findings with pregnancy disorders. The
study results indicate that Doppler sonography is a proven
method for the early detection of decreased uterine perfusion.
The results also show that pregnancies that are at risk for
developing a hypertensive disorder and/or uteroplacental insufficiency can be predicted with increasing confidence in
early pregnancy and that a definite correlation exists with the
development of uterine perfusion during the period of secondary trophoblastic invasion. The results of Steel et al.
11
in particular indicate that the sensitivity of early Doppler ultrasound
screening correlates with the severity of the developing pregnancy disorder.
An abnormal uterine artery Doppler finding may also reflect the presence of chromosomal and/or fetal anomalies,
however (reference 1 and authors’ studies). Kuhlmann et al.
claim that the cause is placental undervascularization resulting from arrested or delayed angiopoiesis.
Obstetric Ultrasound
8
127
Screen for Preeclampsia and Uteroplacental Insufficiency
How to proceed when decreased uterine perfusion is found.
The diagnosis of decreased uterine perfusion warrants further
testing and also a therapeutic response. When anomalies have
been excluded, treatment may consist of a recommendation
for rest, early hemodilution, or aspirin therapy. There are still
no definitive data on the most effective treatment options.
We recommend that the following steps be taken when
decreased uterine perfusion is diagnosed in the 19th or 20th
week of gestation:
➤
Exclude a chromosomal and/or fetal anomaly.
➤
Recommend physical rest.
➤
Treatment with aspirin, hemodilution, or NO donors may be
tried in controlled studies.
➤
Reexamine the patient at 24 weeks. If uterine perfusion is
still decreased, continue treatment with close-interval pregnancy surveillance.
Summary
Characteristic changes in the Doppler sonogram. Doppler
sonography of the uterine vessels is proving to be a suitable
14
method for assessing the development of the terminal uterine
vascular branches to a low-impedance system and for indirectly following the progression of morphological changes,
especially in the spiral arteries. The characteristic changes in
the Doppler sonogram consist of a relativelygreater increase in
frequency shifts during the diastolic phase of the cardiac cycle
compared with systole. This causes a decrease in Doppler indices until the middle of the pregnancy and a disappearance of
the early diastolic notch (on average, during postmenstrual
weeks 16–18).
Given the high variability of Doppler waveforms during the
first trimester, it is not possible to discriminate between normal and abnormal perfusion until the start of the second
trimester.
Diagnostic accuracy. The diagnostic accuracy of Doppler sonography increases with advancing gestation and is maximal between weeks 19 and 24. At this time a definite correlation exists between an abnormal Doppler sonogram and the subsequent development of preeclampsia and/or uteroplacental
insufficiency.
The diagnostic value of early Doppler scanning of the
uterine arteries is that pregnancy complications can be detected at an early stage and therapeutic measures can be instituted to prolong the pregnancy. The ultimate goal is to reduce
the high morbidity and mortality of very early prematurity. Effective treatment options still need to be developed and evaluated, however.
Screening. It remains unclear whether Doppler sonography
should be used as a routine screening test. It seems prudent to
include examination of the uterine vessels in routine screening
at 19–22 weeks, even in patients who have no obvious risk factors.
The early diagnosis of pronounced uteroplacental insufficiency brings us closer to the goal of reducing the high morbidity and mortality of early prematurity by prolonging the pregnancy. Effective treatment options still need to be developed
and evaluated.
References
1 Aristidou A, van den Hof MC, Campbell S, Nicolaides K: Uterine artery
Doppler in the investigation of pregnancies with raised maternal
serum alphafetoprotein. Brit. J. Obstet. Gynaecol. 97 (1990) 431
2 Bieniarz J, Yoshida T, Romero-Salinas G, Curuchet E, Caldeyro-Barcia R,
Crottogini JJ: Aortacaval compression by the uterus in late human
pregnancy.IV. Circulatory homeostatis by preferential perfusion of the
placenta. Amer. J. Obstet. Gynecol. 103 (1969) 19
3 Brosens I, Robertson VB, Dixon HG: The physiological response of the
vessels of the placental bed to normal pregnancy. J. Pathol. Bacterial 93
(1967) 569
4 De Ziegler D, Bessis R, Frydman R: Vascular resistance of uterine arter-
ies: physiological effects of estradiol and progesterone. Fertil. Steril. 55
(1991) 775
5 Funk A, Jörn H, Fendel H: Abdominale versus transvaginale Doppler-
Sonographie der uterinen Gefäße. Ultrasch. Klin. Prax. 7 (1992) 264
6 Goswamy RK, Steptoe PC: Doppler ultrasound studies of the uterine
arteries in spontaneous ovarian cycles. Hum. Reprod. 3 (1988) 721
7 Hustin J, Schaaps J-P: Echocardiographic and anatomic studies of the
maternotrophoblastic border during the first trimester of pregnancy.
Amer. J. Obstet. Gynecol. 157 (1987) 162
8 Kuhlmann RS, Werner AL, Abramowicz J, Warsoff SL, Arrington J, Levy
DL: Placental histology in fetuses between 18 and 23 weeks› gestation
with abnormal karyotyp. Amer. J. Obstet. Gynecol. 163 (1990) 1264
9 Perrot-Applanat M, Groyer-Picart MT, Garcia E, Lorenzo F, Milgram E:
Immunocytochemical demonstration of estrogen and progesterone
receptors in muscel cells of uterine arteries in rabbits and humans. Endocrinology 123 (1988) 1511
10 Rudolph AM, Heyman MA: Circulatory changes during growth in fetal
lamb. Circ. Res. 26 (1970) 289
11 Steel SA, Pearce JM, Mc Parland J, Chamberlain GVP: Early doppler ul-
trasound screening in prediction of hypertensive disorders of pregnancy. The Lancet 335 (1990) 1548
12 Weiner Z, Thaler I, Levron J, Lewit N, Itskovity-Eldor J: Assessment of
ovarian and uterine blood flow by transvaginal color Doppler in ovarian-stimulated women correlation with the number of follicles and
steroid hormone levels. Fertil. Steril. 59 (1993) 743
128
Normal Fetomaternal Doppler Indices in the Second and
15
Third Trimesters of Pregnancy
A. K. Ertan, H. J. Hendrik, I. Tossounidis, and W. Schmidt
Establishing Normal Curves
The goal of defining normal values for fetomaternal perfusion
is to be able to discriminate between normal and abnormal
pregnancies on the basis of Doppler ultrasound findings. This
requires the establishment of reference values and normal
values for physiological conditions of flow
“Ideal” course of pregnancy. Not infrequently, normal values
are based on data from pregnancies that must meet a set of
normal criteria and thus represent more of an “ideal” case. Because of this selection effect, the defined cutoff limits may be
too narrow for at best they describe the variability of “ideal
values” rather than the original biological scatter
Dependence on gestational age. Perfusion changes have been
described with advancing gestation due to maturation of the
trophoblastic tissue, and these changes must be considered in
the interpretation of reference curves. It is best, therefore, to
use gestational-age-based charts to express the normal values
for particular indices. Measurements should commence at a
stage of the pregnancy when the results of the measurements
can still influence obstetric management. The current consen-
8
.
27
.
sus is that this is the mid-second trimester of pregnancy, when
fetal viability is reached. There are also cases in which the
analysis of maternal arterial waveforms can be rewarding in
earlier weeks of pregnancy
Cross-sectional studies. In a cross-sectional study design, the
measurements should be spaced as evenly as possible over the
study period, obtaining an adequate number of measurements
for the various weeks of pregnancy, such as more than 15 per
13
week
pregnancy as this might narrow the tolerance ranges by reducing the variability relative to the natural biological scatter
more favorable prognosis for pregnancies that are at risk by
their history and/or findings but exhibit normal blood flow
patterns. This also requires the analysis of populations with abnormal pregnancies
signed to show the distribution of normal values for the Doppler indices that are most commonly used to characterize fetomaternal blood flow.
. It is best to avoid multiple measurements in any one
The goal of establishing normal reference curves is to offer a
16
.
20
. The curves presented below are de-
9
.
Obstetric Ultrasound
Methodology
Defining the Normal Population
Our normal population consisted of patients whose dates had
been confirmed by an ultrasound examination before the 20th
week of pregnancy. We excluded cases that had a primary cesarean section for placental insufficiency and cases with an abnormal fetal heart rate (FHR) trace or impending intrauterine
asphyxia. The birthweights in the normal population were between the 10th and 90th percentiles for gestational age as defined as Roemer et al.
were 7 or higher, and the umbilical artery pH was 7.20 or
higher. We also excluded multiple pregnancies and cases with
fetal anomalies.
Plotting Quantile Curves
Indices. The qualitative analysis of recorded Doppler wave-
forms has proved to be a more useful clinical tool than the
more complex calculation of volume flow. This is reasonable
18
. The 5- and 10-minute Apgar scores
when we consider that a quantitative analysis requires the
measurement of small vascular cross sections, and this adds a
potential source of error.
Numerous indices have been devised for the qualitative
analysis of Doppler waveforms (review in reference 8). The following are the most commonly used (Fig.15.
➤
The S/D ratio of Stuart (1980)
➤
The resistance index (RI) of Pourcelot (1974)
➤
The pulsatility index (PI) of Gosling and King (1977)
The following quantities are used in analyzing the Doppler
sonogram and calculating the indices:
S = maximum peak systolic frequency
D = maximum end-diastolic frequency
Tav = temporal average of maximum frequency
D = instantaneous spatial average frequency
E = temporal average of spatial average frequencies
22
1):
17
11
129
Normal Fetomaternal Doppler Indices in the Second and Third Trimesters of Pregnancy
In some ultrasound systems, the temporal average of the maxi-
kHz
S/D ratio =
Resistance Iindex(RI):
S–D
Tav
S
D
Time
S
Pulsatility index (PI):
S–D
Tav
S
D
Fig. 15.1 Parameters used for qualitative waveform analysis.
S = maximum systolic frequency, D = maximum end-diastolic
frequency, Tav = temporal average of maximum frequency.
The indices are calculated from the maximum systolic (S) and
end-diastolic (D) frequency shifts and, in the case of the PI,
from the maximum frequency shift averaged over the entire
cardiac cycle (Tav) using these formulas (Fig. 15.
S/D ratio=
15
RI =
S
D
S–D
1):
S
S–D
PI =
Tav
mum frequencies (E) is used in calculating the PI. This results in
correspondingly higher values.
In the studies published to date, no definite advantage has
been found for any single parameter
dices express a ratio, they are largely independent of the insonation angle. The S/D ratio is very easy to determine, and the
RI is easy to interpret: values close to 0 signify a very low flow
resistance, while a value of 1 indicates cessation of flow. The PI,
however, is the only index that can provide differentiated information on an absence of end-diastolic flow, because the
average maximum frequency shift contains information on the
cardiac cycle as a whole, while the S/D ratio tends towardinfinity and the RI equals 1 in cases with absent end-diastolic flow.
Quantiles. Our calculation of normal values was based on 602
pulsed Doppler flow measurements in 370 patients who met
the normal population criteria defined above. An average of
1.62 measurements were acquired per patient. Quan tiles were
determined as a function of gestational age, since the Doppler
values did not show a normal distribution. The study period
was divided into intervals of two consecutive gestational
weeks each, and the 5th, 10th, 50th, 90th, and 95th quantiles
were calculated and plotted graphically for each interval. The
curves were smoothed by cubic regression. In the first example
given below, both the smoothed and original curves are shown.
Since the smoothing did not significantly alter the curve shape,
only the smoothed curves are presented in the figures below.
Th e 5th, 10th, 50th, 90th, and 95th quantiles are shown for
each of the measured indices.
6, 8, 9–11
. Because all the in-
Results
Figures 15.2–15.14 show the reference curves obtained for the
S/D ratio, PI, and RI of the umbilical artery, fetal aorta, middle
6
5
4
Umbilical artery
S/D
3
2
1
0
26
28 30 34
32 36 38 40 42
Weeks of gestation
p95
p90
p50
p10
p5
cerebral artery, and uterine artery. Figure 15.
erence curves for the cerebroplacental ratio.
6
5
4
Umbilical artery
S/D
3
2
1
0
28 30 34
26
32 36 38 40 42
Weeks of gestation
15 shows the ref-
p95
p90
p50
p10
p5
130
Fig. 15.2 Reference curves for the S/D ratio of the umbilical artery,
based on 600 measurements in normal pregnancies and grouped by
even gestational weeks.
Fig. 15.3 Reference curves for the S/D ratio of the umbilical artery,
based on 600 measurements in normal pregnancies and grouped by
even gestational weeks. The curves were smoothed by cubic regression.
Results
1.0
0.8
0.6
Umbilical artery
RI
0.4
0.2
0
28 30 34
26
32 36 38 40 42
Weeks of gestation
p95
p90
p50
p10
p5
Fig. 15.4 Reference curves for the RI of the umbilical artery, based
on 600 measurements in normal pregnancies and grouped by even
gestational weeks. The curves were smoothed by cubic regression.
12
10
Fetal aorta
8
6
S/D
4
2
p95
p90
p50
p10
p5
1.8
1.6
1.2
Umbilical artery
PI
0.8
0.4
0
26
28 30 34
32 36 38 40 42
Weeks of gestation
p95
p90
p50
p10
p5
Fig. 15.5 Reference curves for the PI of the umbilical artery, based
on 510 measurements in normal pregnancies and grouped by even
gestational weeks. The curves were smoothed by cubic regression.
1.0
0.8
Fetal aorta
0.6
RI
0.4
0.2
p95
p90
p50
p10
p5
Obstetric Ultrasound
0
28 30 34
26
32 36 38 40 42
Weeks of gestation
Fig. 15.6 Reference curves for the S/D ratio of the fetal aorta,
smoothed by cubic regression.
3.0
2.5
Fetal aorta
2.0
PI
1.5
1.0
0.5
0
28 30 34
26
32 36 38 40 42
Weeks of gestation
p95
p90
p50
p10
p5
0
28 30 34
26
32 36 38 40 42
Weeks of gestation
Fig. 15.7 Reference curves for the RI of the fetal aorta, smoothedby
cubic regression.
14
12
10
8
S/D
6
Middle cerebral artery
4
2
0
28 30 34
26
32 36 38 40 42
Weeks of gestation
p95
p90
p50
p10
p5
Fig. 15.8 Reference curves for the PI of the fetal aorta, smoothed by
cubic regression.
Fig. 15.9 Reference curves for the S/D ratio of the middle cerebral
artery, smoothed by cubic regression.
131