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a Chapter 26 Doppler Velocimetry for Fetal Surveillance: Randomized Clinical Trials and Implications for Practice 393
Objective and Primary Outcome
Considerable variation was also noted in the purpose
of the trials and the measures of the primary outcome.
Many of the studies measured various outcomes
related to pregnancy management, fetal surveillance,
management of labor and delivery, and
perinatal morbidity and mortality. Lack of uniformity,
however, was apparent with regard to the specific
criteria of these measures. Among the rest, the
objective of one was to assess physicians' use of Doppler
information [9], and that of the other was to
evaluate the effect of Doppler testing on the time required
for fetal assessment [3]. Only half the studies
reported a predetermined, specific primary outcome
measure.
Doppler Sonographic Technique
and Research Design
Although it may be difficult to expect a significant
degree of dissimilarity in the instrumentation and
procedure for Doppler interrogation of the umbilical
arteries, there are some aspects of the method that
can become critical sources of variance in results.
They include the Doppler mode and the high-pass filter,
a high level of which may produce false identification
of AEDV. Many studies utilized continuouswave
Doppler ultrasound, while others used pulsedwave
Doppler mode, or did not specify the type of
Doppler setup used for the study. One trial [12] utilized
a 280-Hz high-pass filter setting; interestingly,
this study reported the highest occurrence of AEDV.
Five studies did not state the filter setting, and the
rest utilized a threshold of 50±100 Hz. With regard to
the use of Doppler sonography in the trial design,
four studies [1, 4, 13, 32] used a Doppler technique
in all patients, but the results were revealed to the obstetric
care providers only for the study group. There
is no measure, however, of the success rate for concealing
Doppler information for the control group. In
three studies [2, 3, 10] Doppler sonography was used
in the control group in a selective manner, which was
not uniform among the studies. In the remainder of
the trials, Doppler sonography was not supposed to
be performed in the control group of patients,
although this ªruleº was not universally implemented.
Management Protocol
Management protocol probably represents the most
problematic source of clinical heterogeneity in these
trials. Only seven of the studies had predefined treatment
protocols [6, 11, 12]. The rest had limited or no
set protocol for management; the results were given
to the care providers, and it was anticipated that they
would exercise their experience and knowledge to
make the best use of this information. Others may
have had some guidelines, but it was not apparent in
the paper. This drawback severely limits the utility of
these trials for formulating any evidence-based fetal
surveillance policy utilizing Doppler ultasonography.
Doppler Randomized Trials:
Meta-Analysis
Meta-Analysis: Brief Introduction
Although the traditional review of the published clinical
trials of Doppler velocimetry as presented above
is informative, it does not help to arrive at a definitive
conclusion regarding its efficacy, nor does it provide
us with a reasonable basis for developing a management
plan. Even if Doppler sonography is highly
effective, a traditional review fails to give us a measure
of the magnitude of benefit that may result from
its use in clinical practice for fetal surveillance. These
problems can be significantly mitigated by performing
a more systematic review by aggregating and statistically
analyzing data from the various trials to derive
a valid quantitative conclusion. The process is
called meta-analysis, a term coined by Glass [34] to
distinguish it from the primary analysis, which is the
original process of analyzing the information from an
individual research study, and from the secondary
analysis, which is reanalysis of the original data to
address new research questions. The concept is not
entirely new, as quantitative statistical synthesis of
past research data was described by several eminent
statisticians decades before the origin of the term
meta-analysis [35±37].
The technique has been used widely for systematic
review of scientific research in the social sciences and
was applied extensively later to clinical research in
medicine. As the number of clinical trials has mushroomed,
the need to depart from the more traditional
subjective, often inconclusive review process has
grown. The application of this type of quantitative
systematic review of published data has been slow in
the field of obstetrics. One of the key elements for
popularizing this approach in obstetrics and gynecology
has been the effort of the Oxford Perinatal Data
Group and its inheritor, the Cochrane Perinatal Collaboration
in the United Kingdom. An in-depth discussion
of meta-analysis is beyond the scope of this
chapter, but a brief review, specifically relevant to
Doppler trials, is included here. It should be noted
that this concise discussion is limited to the metaanalysis
of experimental studies, such as randomized
clinical trials, and excludes meta-analysis of nonexperimental
investigations or observational studies,