o_1977r8vv9vk1ts2ms0kd8pksa.pdf

304 H. Odendaal
were most frequently the primary cause for the abnormal
flow velocity [48]. It is important to note that
third-trimester fetal growth rate correlated better
with intrapartum fetal distress than fetal size alone
[79]. The same principle could be applied to Doppler
flow velocity waveforms, where abnormal flow velocity
is of greater significance than calculated fetal
weight.
Umbilical Artery Flow Velocity Waveforms
in Low-Risk Populations
Routine use of umbilical Doppler in low-risk pregnancy
is not recommended [28, 37]. These findings
are also supported by a Cochrane Library review of
the findings in 14,338 women in 5 studies [14].
Umbilical Artery Flow Velocity Waveforms
in High-Risk Pregnancy
In 1995 Alfirevic and Neilson [5] published their first
systematic review with meta-analysis and concluded
that women with high-risk pregnancies, including
pre-eclampsia and suspected IUGR, should have access
to Doppler flow velocity waveform examinations.
In a more recent study [70], they examined eleven
good quality trials in nearly 7,000 women. Most of
the causes for the high-risk pregnancy were hypertension
and presumed poor fetal growth. There was a
trend towards a reduction in perinatal deaths (odds
ratio 0.71, 95% CI 0.50±1.01). Use of Doppler ultrasound
was also associated with fewer inductions of
labor (odds ratio 0.83, 95% CI 0.70±0.93) and fewer
admissions to hospital (odds ratio 0.56, 95% CI 0.43±
0.72).
More recently, Westergaard et al. [104] only considered
well-defined studies; 1,307 patients had suspected
IUGR and 852 had IUGR and/or hypertension. There
were 13 RCTs in 8,633 mothers. These well-defined
studies showed significant reductions in antenatal admissions,
inductions of labor, elective deliveries, and
caesarean sections with the use of umbilical Doppler
velocimetry. More perinatal deaths were potentially
avoidable by Doppler velocimetry (p< 0.0005).
Doppler Ultrasound and HELLP Syndrome
Joern et al. [47] investigated the umbilical artery,
both uterine arteries and the middle cerebral artery
in patients with different grades of hypertension. The
worst perinatal outcome was found when all four vessels
were abnormal. The largest proportion of abnormalities
was in the women with HELLP syndrome.
Bush et al. [15] studied 50 women with HELLP syndrome.
Although abnormal umbilical artery velocimetry
was associated with a high likelihood of delivery
by cesarean section, the Doppler findings did not correlate
with the severity of maternal disease.
Effect of Antenatal Steroids
As many patients with severe pre-eclampsia need delivery
before fetal pulmonary maturity has been
reached, administration of steroids is strongly indicated
before delivery is considered. It has been established
that the administration of steroids is indeed
safe in patients with severe pre-eclampsia [89]. It
should be kept in mind that betamethasone treatment
has been associated with a temporary (2±7 days) decrease
in placental vascular resistance [103]. Other
ways of fetal assessment, such as fetal heart rate
monitoring, should therefore be relied upon during
this period.
Fetal Assessment Before Admission to
Hospital
There are many forms of fetal assessment in mothers
with hypertension in pregnancy such as the biophysical
profile [62], amniotic fluid volume assessment
and Doppler flow velocity studies in other fetal and
maternal vessels [24, 57, 80, 93]. Many of these are
time-consuming, need sophisticated instrumentation
and are difficult to interpret. It is also necessary,
especially from the point of view of a developing
country, to limit unnecessary expenditure. For this
reason we prefer Doppler flow velocity of the umbilical
artery as the screening test in high-risk pregnancies
as identified by hypertension or poor symphysis
pubis growth [95].
Based on the nomogram of Tygerberg Hospital
[82, 83], the 50th percentile was initially regarded as
the cut-off line for normality. As few fetal complications
were observed when the RI fell between the
50th and 75th percentile lines, the 75th and 95th percentiles
are now accepted as the dividing lines. The
green area below the 75th line is regarded as normal
(Fig. 19.3). No further tests for placental function are
indicated unless there is a change in the clinical condition
of the mother. The orange area between the
75th and 95th percentiles indicates uncertainty. The
test should be repeated after 2 weeks and the fetal
heart rate pattern recorded immediately and at all
subsequent visits. The red area above the 95th percentile
indicates that the Doppler should be repeated
weekly and that a non-stress test should be done
twice a week. Absent end-diastolic flow velocity in
the umbilical artery is an indication for admission to
hospital for intensive fetal monitoring or delivery, depending
on the gestational age.