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Umbilical Cord Complications and Doppler Ultrasound
Table 14.1 Elucidation of umbilical cord findings by various ul­trasound procedures
Umbilical cord finding Ultrasound procedures suit-
able for displaying finding
Localization Gray-scale B-mode image/
color Doppler ultrasound Number of perfused vessels Color Doppler ultrasound Thickness of umbilical cord Gray-scale B-mode image Flow restriction Doppler sonogram
(waveform)/color Doppler
ultrasound
Fig. 14.3 Late systolic notch on the waveform of the umbilical a., possibly caused by a knot in the umbilical cord.
134
blubber
Umbilical Cord Complications and Doppler Ultrasound

Obstetric Applications of Doppler Ultrasound: References

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Advanced Topics
in Obstetrics and
Gynecological
Doppler Ultrasound
Advanced Topics
137
3
138

15 Doppler Ultrasound and the Cardiotocogram

Increased impedance values in the umbilical aa. and the fetal aorta correlate well with fetal asphyxia. The link between the diagnostic significance of Doppler flow curves and an abnormal antepartum cardiotoco-
gram (CTG) can only be examined when fetal asphyxia
is due to chronic placental insufficiency. Reduced
Apgar scores at 5 minutes or acidotic pH values can only be used as criteria for fetal asphyxia in primary cesarean sections, since it is very unlikely that fetal hy­poxia was present before delivery in infants who have survived vaginal delivery or even a secondary section after hours of labor. A consideration in such cases is that asphyxia may be induced by umbilical cord com­plications during the first stage of labor or the second stage, even when blood supply to the fetus was pre-
viously undisturbed.
Attempts to interpret abnormal Doppler findings as opposed to abnormal CTGs lead to different prognostic evaluations of the condition of the fetus. The Doppler

Comparing Tests

Table 15.1 Cardiotocogram and Doppler ultrasound
A normal CTG
reflects the circulation and cerebral function of the fetus.
A highly abnormal CTG
expresses a change in fetal cerebral function.
A Doppler sonogram
reflects the circulation in a vascular region.
Circulation Cerebral function
Normal CTG 쐌쐌 Highly abnormal CTG Doppler sonogram
sonogram displays the resistance in the fetoplacental and uteroplacental circulation and is thus a chronic parameter. An abnormal CTG displays hypoxic changes in the fetal brain and is therefore an acute parameter. When comparing the validity of the two methods these differences between them must be borne in
Table
mind (
15.1).
Advanced Topics
Comparing Tests to Predict Neonatal
Asphyxia
An overview of the literature evaluating the CTG as a basis for obstetric decision-making reveals a high false positive rate, though specificity is good. Comparison of the studies is made more difficult by the different com­position and size of the populations studied (preva­lence). A clinical study by Krebs (1978) using Fischer scores improved the results by reducing the rates of false positives. The design of the studies shown in
T
15.2 makes it possible to compare them.
able
15.3 shows the results of a study comparing
Table the reliability of predictions of neonatal asphyxia by CTG and umbilical cord Doppler sonography. Doppler flow measurements showed a slight superiority be­cause of their higher sensitivity. In all three studies sensitivity was shown to be superior to CTG (by reduc­tion in the false positive rate). At the same time speci­ficity was slightly lower (because of a slight increase in false positive results). According to these studies the Doppler procedure seems to be more sensitive.
Tabelle 15.2 Prediction of neonatal asphyxia by CTG
Author Year Sensitivity Specificity
Flynn and Kelly 1977 59 % 85 % Krebs 1978 54% 98% Keane 1981 54% 87% Our results 1991 69% 89%
Table 15.3 Comparison of the validity of predictions of neonatal asphyxia by CTG and Doppler ultrasound examination of the umbilical a.
Author Sensitivity
Trudinger et al. 1986
Weiss et al. 1989
Our results 199 1
Specificity %
Sensitivity % Specificity %
Sensitivity % Specificity %
Sensitivity % Specificity %
CTG Doppler
36 88
67 74
69 89
UA
60 85
87 67
76 85
139
Doppler Ultrasound and the Cardiotocogram
3
Table 15.4 Comparison of the validity of predictions of neonatal acidosis by CTG and Doppler ultrasound examination of the umbilical a.
Author Sensitivity
Specificity
Weiss et al. 1989 Sensitivity %
Specificity %6774
Our results 1991 Sensitivity %
Specificity %8189
CTG Doppler
umbilical a.
87 67
84 84
Comparing Tests to Predict Neonatal Acidosis
Comparisons between tests that predict neonatal acid­osis are not subject to the considerations applied to Apgar scores. While lower Apgar scores are thought to be more prevalent in a population that includes a higher proportion of premature births and cesarean sections, the pH of the umbilical cord is considered to be a more objective parameter. Table superiority of Doppler ultrasound, which is more sen­sitive, though this is again achieved at the cost of a re­duced specificity (greater rate of false positives).

Information Lead Time Using Doppler Ultrasound

A test with greater lead time in providing information relevant to a later event can contribute greatly to the improvement of obstetric monitoring and decision­making. This is especially true of tests that capture and monitor fetal risks developing over time into chronic conditions. These conditions include growth restric­tion due to placental insufficiency, multiple pregnan­cies with discordant growth, and hypertension of preg­nancy. Before the introduction of Doppler ultrasound, the CTG was the method of choice for monitoring preg­nancies that carried an increased perinatal risk.
%
100
90
80
70
60
50
40
30
20
10
0
< 1 1-2 3-5 6-10 11-30 31-50 Days
an early warning system when monitoring a high-risk population before delivery, we examined in our own population the interval from the first sign of an abnor­mal Doppler finding in the umbilical a. (reading of
97% of the normal curve) to the development of an
abnormal CTG and the indication for a primary ces­arean section ( curve shows an interval of three to five days and more (up to 50 days) in 50% of this population. In 85% of cases the interval was 24−48 hours, an interval that gives an obstetric attendant a relatively long time to prepare. In 15% of cases action was required on the same day. This is a frequent observation in perinatal centers, where high-risk patients arrive from outlying clinics at short notice. The longest time intervals, i. e., the earliest advance warning compared to the CTG, was obtained when Doppler ultrasound was intro­duced at the earliest possible moment, for example, at the first hint of an impending problem, or when the risk was suggested by history. In a literature review Schneider et al. (1989) give an average time interval of seven days. Laurin et al. (1987) and Jouppila et al. (1986), who managed a caseload similar to our own, agreed that the median interval was three days.
Fig. 15.1 Relative incidence of time intervals from the first ab-
normal Doppler record in the umbilical a. to the development of
an abnormal CTG and the indication for primary cesarean sec­tion (after Voigt 1991).
15.4 shows the
In order to test if Doppler ultrasound can be used as
F
ig.
15.1). The cumulative percentage
140

Clinical Significance of Doppler Ultrasound

Clinical Significance of Doppler Ultrasound
The clinical significance of any new monitoring pro-
cedure in obstetrics can be judged by whether it pro-
vides a better basis for decision-making and improves the condition of the neonate. Until the development and validation of our own reference curves we could only use retrospective reviews of study results. Once obstetric attendants became aware of these Doppler findings, they were able to use them to assess clinical abnormalities and to make decisions, and prospective studies became a reality. Since the previously estab­lished monitoring procedures and pediatric manage­ment did not change, it was possible to compare popu­lations studied retrospectively and prospectively.
5.5 and 15.6 sho
bles 1
w the results of this comparison.
Ta-
In this study no significant differences between
groups were found when flows were normal. When Doppler findings were abnormal, both populations re­quired early delivery equally, on average at 34−35
weeks of gestation.
As regards type of delivery, in the prospective group cesarean sections for asphyxia declined from 20% to 6%, emergency cesarean sections increased from 14.8% to 23.9%, and elective cesarean sections from 18.5% to
30%. From these significant differences it can be con­cluded that in the prospective group the obstetric at­tendant was less frequently surprised by a threatening asphyxia. When the circumstances leading to emer-
gency cesarean sections were examined, oxytocin augmentation or induction of labor with prostaglandin and stand-by cesarean section were found more frequently. The clear increase in the rate of elective cesarean sections demonstrated that the clinical situa­tion often led to elective cesarean section before the need to resort to emergency cesarean section.
Where Doppler findings were abnormal in the
younger population, the incidence of acidosis was sig­nificantly lower and could no longer be distinguished from that of populations with normal flow rates. The difference previously noted could no longer be demon-
15.7).
strated (
Table
Hence it remains established that Doppler sonogra­phy is an outstanding “early warning system” for a slowly developing threat to fetal well-being resulting from chronically impaired nutritional supply. In such cases it offers advance warning of several days before the CTG. Moreover,it can lead to a significant reduction in the incidence of acidosis if the Doppler findings are considered when making decisions regarding the type of delivery.
However, we wish to point out again that threats to the fetus arising acutely, such as acute placental in-
Table 15.5 Comparison of the history of one population ex­amined “retrospectively” and one examined “prospectively” by Doppler ultrasound. “Retrospective” means that a Doppler ex­amination was performed, but no conclusions were drawn from it; “prospective” means that the Doppler finding contributed materially to the decision regarding the mode of delivery.
Doppler finding
Umbilical a. Delivery weeks 39.5 40 n.s. Doppler
finding
normal Median UA pH 7.27 7.29 n.s. Umbilical a. Delivery weeks 34.4 35 n.s.
Doppler
finding
abnormal Median UA pH 7.23 7.28 *
Parameter Population examined
Mode of delivery
Mode of delivery
Retro­spective
n.s.
Table 15.6 Table 15.6 *
Pro­spective
n.s. = not significant * p 쏝0.5
Table 15.6 Rate and type of section in the “retrospective” and “prospective” populations with abnormal Doppler findings
Rate and type of section Population examined
Section rate 53.3% 59.9% n.s. Emergency section,
section for asphyxia Urgent section 14.8% 23.9% * Elective section 18.5% 30% *
Retrospective Prospective
20% 6% **
n.s. = not significant * p ⬍ 0,05 ** p ⬍ 0,01
Table 15.7 pH values in the umbilical arteries of the “retro­spective” and “prospective” populations with abnormal Dop­pler findings
Doppler finding
Umbilical a Median n.s. Doppler
finding normal (range) (7.13−7.40) Umbilical a Median * Doppler
finding abnormal (range) (6.98−7.32) (7.08−7.38)
pH value in umbilical a.
umbilical a. pH 7.27 7.29
umbilical a. pH 7.23 7.28
Population examined Retro­spective
Pro­spective
n.s. = not significant * p 쏝0.5
sufficiency in a previously normal pregnancy, cannot be detected by Doppler examination, especially after the 38th week of pregnancy (cf.
Chap
16, p. 143). In
ter
this situation CTG is clearly superior.
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16 Doppler Ultrasound Findings Near Term

To estimate the time of delivery and determine whether the fetus is postterm, an ultrasound examina-
tion must be performed early in pregnancy. It should
include crown−rump measurement and correction of gestational age if indicated.

Physiological Findings in the Late Stages of Pregnancy

Late pregnancy and delivery are marked by increased demands by the fetus with only minimal growth of the supply organ, the placenta.
The blood flow rate in the uterine aa. increases steadily throughout pregnancy, from 190 mL/min before pregnancy to about 680 mL/min in late preg­nancy. The mean diameter of the uterine a. expands from 1.6 mm before pregnancy to 3.7 mm near term.
The ratio of the mean peak systolic velocity to the mean maximal end-diastolic velocity decreases from a mean value in the non-pregnant woman of 5.3 (re­sistance index [RI]: 0.81) to 2.3 (RI: 0.57) near term.
The mass of the placenta increases steadily from about 6 g at six weeks’ amenorrhea to over 500 g at term. The fetus grows considerably faster than the placenta, with the result that the ratio of the weight of the placenta to that of the fetus decreases from 1.16 at 16weeks to 0.13 at term. Very early Doppler recordings show a rise of mean placental perfusion in the course of pregnancy from ca. 100 mL/min at 22 weeks of ge­station to a maximum of over 320 mL/min at 37−38
weeks. After that the last two weeks show a regression to ca. 300 mL/min. The relation of the infant’s weight to blood flow volume is constant at 120 mL/kg/min until the 36th to 37th week of pregnancy. During the final stage of pregnancy this number, too, may regress to 90 mL/kg/min. At the same time the RI declines from
0.6 at 28 weeks of gestation to 0.5 at term.
Concurrently,the quantity of amniotic fluid declines, and the vernix caseosa disappears from the fetal skin, a sign that the nutritive function of the placenta is re­duced.
The signs of maternal adaptation to the pregnancy
gradually disappear: The hematocrit rises again, the blood pressure returns to its value before the preg­nancy, the sensitivity to angiotensin II returns to nor­mal values, and edema of pregnancy may subside.
The conditions affecting the responses of the fetal circulation include a relative reduction in placental tissue available for nutrition and gas exchange, as
well as an absolute reduction in fetoplacental blood flow.
Aorta: Quantitative Analysis
In the early years of Doppler ultrasound use in ob­stetrics, quantitative measurements were obtained from the uteroplacentofetal unit. The largest vessel that can be accessed easily is the aorta. Hence one of the first reported results was that of a relative blood flow in the descending aorta of 185 (7.6)mL/min/kg estimated fetal weight.
A number of groups determined and published other parameters during the course of pregnancy. Mean blood flow velocity (temporal average of spatial aver­age velocity [TASAV]) ran between 26.5 cm/s and
34.6 cm/s, with a median of 29.0 cm/s. The relative mean blood flow amounted to between 169 mL/min/ kg and 246 mL/min/kg, with a median of 220 mL/min/ kg. The systolic peak velocity (Mv 70 cm/s and 118 cm/s, with a median of 100 cm/s. At term mean aortic stroke volume was reported to be 5.4 (1.6) mL, the relative aortic stroke volume 1.8 (0.5) mL. The mean systolic diameter of the aorta was 7.3 (
1.1) mm, the mean diastolic diameter 6.3 (1.1) mm. The mean effective aortic diameter, determined by echo markers, was 7.0 (1.1) mm.
In our own study of blood flow in the descending aorta we found that most values increased between the 24th week of gestation and delivery, though the range was wide.
All quantitative determinations of blood flow, then, varied widely both in normal and abnormal pregnan­cies. One reason for this was the equivocal and impre­cise determination of the diameter of fetal blood ves­sels by ultrasound. Clinicians were disappointed, since their expectation that ultrasound would provide them with a precise method to measure blood flows was not fulfilled.
) was between
max
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