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a Chapter 24 Doppler Velocimetry for Fetal Surveillance: Adverse Perinatal Outcome and Fetal Hypoxia 367
that of the currently utilized fetal surveillance procedures.
This section presents the comparative effectiveness
of these modalities in relation to the prediction
of adverse perinatal outcome. Other relevant aspects
of this issue (i.e., the prediction of fetal asphyxia and
the sequence of occurrence of abnormal tests) are
discussed later in the chapter.
The effectiveness of the umbilical arterial A/B (S/D)
ratio for predicting adverse outcome was investigated
by Trudinger et al. [2] in 170 high-risk patients. The
parameters of fetal compromise included birth weight
below the 10th percentile or an Apgar score of less than
7 at 5 min. The fetal heart rate was assessed in terms of
reactivity and a modified Fischer score. In this study,
the umbilical arterial S/D ratio appeared to be more
sensitive, but less specific, than electronic fetal heart
rate monitoring. Farmakides et al. [8] investigated
the diagnostic efficacy of the NST and the umbilical arterial
S/D ratio in 140 pregnancies. The measures of
outcome included intrauterine growth restriction
(IUGR), fetal distress, cesarean section for fetal distress,
and admission to the NICU. Fetuses with a normal
NST but abnormal S/D ratio had an outcome worse
than those with an abnormal NST and a normal S/D ratio;
those for whom both tests were abnormal experienced
the worst outcome.
Further corroboration came from Arduini et al.
[9], who noted in a cross-sectional study involving
1,000 unselected pregnancies at 36±40 weeks' gestation
that umbilical velocimetry was more effective
than NST for identifying fetuses at risk of adverse
outcome (cesarean section for fetal distress, lower
birth weight, 5-min Apgar score < 7, admission to the
NICU). The relative strengths of the individual and
combined use of the various tests were investigated
by Hastie et al. [10] in 50 pregnant patients. These
investigators observed that the repeat nonreactive
NST was highly sensitive (92%) and the S/D ratio
highly specific (83%); they therefore suggested the effectiveness
of combining the two tests for predicting
adverse perinatal outcome. The suggestion of a combined
approach also came from Nordstrom et al.
[11], who determined the umbilical arterial S/D ratio
and biophysical profile in 69 high-risk pregnancies
within 10 days preceding the delivery. Intrapartum fetal
distress and SGA occurred in 43% of the infants.
The S/D ratio demonstrated a higher sensitivity
(37%), specificity (92%), positive predictive value
(PPV) (79%), and negative predictive value (NPV)
(66%) than the biophysical profile (27%, 82%, 53%,
and 59%, respectively).
These observational studies, though highly informative,
do not provide evidence for a greater effectiveness
of any of the tests in regard to altering outcome.
Such conclusions can be achieved only by randomized
trials. This issue is discussed in Chap. 26.
Fetal Doppler Sonography
and Neurodevelopmental Outcome
As indicated above, the currently utilized immediate
measures of outcome may not effectively prognosticate
the long-term effects of in utero fetal compromise
on subsequent neurologic development. This
point is particularly relevant when assessing the efficacy
of antepartum surveillance, which is a relatively
difficult area of investigation. Not surprisingly, there
are few studies in this area, and those published so
far are contradictory. MarÉ—l and Ley [12] in their
long-term investigation found a significant correlation
between the abnormalities of fetal aortic Doppler
waveforms and deficient neurologic development of
the infant assessed at 7 years of age. Similarly, Fouron
et al. [13] measured the ratio of antegrade to retrograde
velocity integrals in the aortic isthmus of 44
fetuses with abnormal umbilical artery Doppler
velocimetry and studied the neurodevelopmental condition
of the children between the ages of 2 and 4
years. The investigators found a significant correlation
between the flow patterns in the fetal aortic isthmus
and neurodevelopmental deficit, with a relative
risk of 2.05 (95% CI 1.49±2.83) when predominantly
retrograde flow was observed in the fetal aortic isthmus.
These findings are significant and require corroboration.
In a group of fetuses from high-risk pregnancies
delivered before 34 weeks Todd et al. [14]
found that when compared with umbilical Doppler
velocimetry, antepartum fetal heart rate monitoring
was more strongly associated with poor cognitive
function of the infant at 2 years of age. Obviously, additional
investigations are required before any definitive
conclusions can be reached on this issue.
Efficacy of Doppler Sonography
for Screening Low-Risk
and Unselected Pregnancies
Although the diagnostic efficacy of the Doppler technique
in a high-risk population is encouraging, its performance
in a low-risk population is disappointing, as
indicated by several studies summarized below.
In a prospective study involving 2,097 singleton
pregnancies, Beattie and Dornan [15] evaluated the
capability of umbilical arterial Doppler indices [pulsatility
index (PI), S/D ratio, resistance index (RI)] to
detect fetal growth restriction and perinatal compromise.
It was noted that the indices did not adequately
predict any of the parameters of adverse perinatal
outcome. It is noteworthy, however, that elevated
Doppler indices were the only abnormal findings in
three cases of unexplained fetal death in this population.
Moreover, although the investigators did not
find the indices to be useful for timing the death,