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a Chapter 19 Doppler Velocimetry and Hypertension 303
Table 19.1. Screening in the second trimester: umbilical artery. SGA small for gestational age, PIH pregnancy-induced
hypertension, IUGR intrauterine growth restriction
Method End points Gestational age (weeks) Reference
Pulsatility index Abruptio placentae 11±14 [87]
IUGR
Pre-eclampsia
Pregnancy-induced hypertension
Resistance index >0.58 SGA 22±24 [21]
Bilateral notches
Abruptio placentae
Pre-eclampsia
PIH
Notch depth index Pre-eclampsia 16±23.9 [77]
SGA
Pulsatility index >1.45 Pre-eclampsia 23
24±36
[4]
[66]
Bilateral notches
Both RI >0.58
Pre-eclampsia
SGA
Gestational hypertension
1. How accurate is the screening?
Not accurate as reflected by the poor sensitivity,
specificity and positive predictive value
2. When should the screening start?
As the prediction is poor, one does not really
know when to screen. From a practical point of
view, the best times to screen are obviously when
pregnancies are routinely screened at 11±14 weeks
or at 20 weeks
3. What is the best method of screening?
The best method is still uncertain, but it seems
that a combination of abnormalities, such as bilateral
notches with a high RI or PI, is preferable.
4. Should any high-risk women be screened?
High-risk women would in any case be put on
low-dose aspirin from early pregnancy. A patient
at high risk according to the obstetrical or medical
history, but at low risk according to uterine artery
Doppler examination, would probably be put on
aspirin; however, the primigravida may benefit
from screening as the outcome of pregnancy would
be more uncertain.
5. Which risks should be identified?
Risks associated with poor placentation should be
determined. They are ªabruptio placentaeº, gestational
hypertension, pre-eclampsia and IUGR.
Small for gestational age should not be regarded
as abnormal because many babies with low birth
weight are constitutionally small.
6. Can intervention in the identified women improve
the outcome of pregnancy?
Early administration of aspirin will improve the outcome
in the majority of high-risk patients.
Umbilical Artery Doppler
Nicolaides et al. [69] examined the oxygen tension
and pH of umbilical cord blood, obtained by cordocentesis,
in 59 fetuses with an abdominal circumference
below the 5th percentile and absent end-diastolic
velocity. Only 7 fetuses had normal oxygen tensions
and pH. This important finding stimulated
further research on the clinical use of umbilical artery
Doppler.
The poor oxygenation of the fetus is most likely to
be caused by deficient development of the villous
structure of the placenta. Volumes and surface areas
of intermediate and terminal villi are reduced [46],
terminal villi are smaller [61] and more stem villi
have medial hyperplasia and laminal obliteration. In
addition, terminal villi are poorly vascularized [85]
and gas-exchanging villi are poorly developed [96].
For the interested reader, there are several very good
review articles which give more detail [3, 8, 40, 49,
51, 78, 84].
Higher endothelin-1 levels are reported in mother
and the fetus complicated by IUGR, but the values
are surprisingly not related to umbilical artery blood
gases. Elevated endothelin-1 levels were significantly
associated with pregnancy-induced hypertension [30].
Abnormal umbilical artery Doppler findings are also
associated with greater nucleated red blood cell
counts, signifying an association with fetal hypoxia
[10].
Clinical Findings
Several studies associated abnormal umbilical artery
Doppler flow velocity waveforms with poor perinatal
outcome [48, 71, 96]. Hypertension and pre-eclampsia