o_1977r8vv9vk1ts2ms0kd8pksa.pdf

356 R. O. Bahado-Singh et al.
Table 23.1. Umbilical artery Doppler: diagnostic performance for adverse outcome in prolonged pregnancies. AEDF absent
end-diastolic flow, PPV positive predictive value, NPV negative predictive value, LR likelihood ratio (sensitivity/falsepositive
rate)
Reference Test Sensitivity (%) Specificity (%) PPV NPV LR a
[8] S/D ³ 2.4 57.1 77.8 50.0 82.4 2.6
[10] AEDF 91 100 91 180 ± a
[12] RI 16.7 96.2 28.6 92.6 4.4
[13] S/D 80 55 30 97 1.8
[4] RI >0.62 37 75 40 73 1.5
a LR =infinity.
their respective false-positive rates (or their specificities).
The various Doppler studies quoted different
specificity values for their reported sensitivities. This
makes it very difficult to compare the diagnostic accuracy
of umbilical Doppler between different studies.
One way of surmounting this limitation is to calculate
the so-called likelihood ratio (LR). The likelihood ratio
is calculated by dividing the sensitivity value by
the false-positive rate. The false-positive rate in turn
is equal to 1±specificity expressed as a decimal or
alternatively 100%±specificity expressed as a percentage.
The higher the LR of a test, the stronger is the
correlation between the test measurement and outcome;
thus, a test with a higher LR is generally a better
test than one with a lower value. Table 23.1 lists
the diagnostic indices of umbilical artery Doppler
velocimetry in prolonged pregnancies from studies
reporting more complete data.
The issue of whether umbilical artery Doppler consistently
predicts adverse outcome in prolonged pregnancy
remains unresolved. Of the 10 studies reviewed,
only three reported increased vascular resistance
identifiable on Doppler in prolonged pregnancy
with adverse outcome. Indeed, one study paradoxically
found a reduction in placental resistance in prolonged
pregnancies as determined by umbilical Doppler.
There is currently insufficient evidence to propose
that Doppler velocimetry of the umbilical artery
should be used in routine management of prolonged
gestation. The significant variability in the design of
these various studies quite predictably makes it impossible
to draw any strong conclusions regarding the
value of umbilical Doppler in prolonged gestations.
The many areas of differences in study designs included
differences in defining prolonged pregnancies,
varying umbilical Doppler thresholds used to define
abnormal variation in ultrasound equipment, and
Doppler modality used, i.e., continuous- vs pulsedwave
Doppler and, most importantly, significant variation
in outcome end points used to define perinatal
complications. Very few of the studies with negative
association performed power analysis. There is a significant
possibility that many of the negative trials
were underpowered.
Umbilical Artery Doppler Versus
Other Antepartum Tests
Currently, the most commonly employed protocols for
the antepartum monitoring of prolonged pregnancies
incorporate the NST and amniotic fluid volume assessment.
A few studies compared umbilical Doppler
velocimetry to these more commonly used tests. In a
study that found a correlation between Doppler and
perinatal complications, Fischer et al. [8] compared
umbilical Doppler S/D to NST and amniotic fluid
measurements (Table 23.2). The umbilical artery Doppler
was a better test than NST and amniotic fluid
volume assessment combined.
In another study that found the umbilical artery to
be a useful predictor of outcome in prolonged pregnancy
Pearce and McParland [10] compared absent
end-diastolic flow velocity (AEDF) umbilical Doppler
to NST and largest fluid pocket < 3 cm for prediction
of fetal distress. The Cohen kappa statistic was used.
Kappa values vary from 0 to 1.0. Values of 0±0.2 denote
test results that may be chance findings, 0.2±0.8
indicates increasing agreement, and values > 0.8 show
strong correlation between the test results and the
outcome of interest. Based on the kappa statistic, umbilical
Doppler AEDF appeared to be a superior predictor
of fetal distress in the first stage of labor compared
with either the NST or amniotic fluid pocket.
Kappa statistic for AEDF, NST, and fluid pocket fetal
distress in the first stage of labor was 0.91, 0.41, and
0.68, respectively. Fluid pocket and Doppler AEDF
were modest predictors of second-stage distress with
NST showing no meaningful correlation with this particular
outcome (kappa values 0.39, 0.29, and 0.05).
All except fluid volume had poor correlation with 5-
min Apgar < 5 (kappa statistic 0.03, 0.07, and 0.37 for
NST, AEDF, and fluid pocket, respectively).
Weiner et al. [12] compared NST, oligohydramnios
(< 5 cm), and umbilical RI > 0.68 for the detection of
perinatal compromise; the latter consisted of 5-min
Apgar < 7, NICU admission, cesarean for fetal distress,
and birth weight less than the 5th percentile.
The umbilical artery Doppler performance based on