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a Chapter 20 Doppler Velocimetry and Multiple Gestation 327
Future Research
The value of Doppler velocimetry in twin and other
pregnancy applications is questioned since this modality
has yet to demonstrate an improvement in
pregnancy outcome by prospective studies [115].
While this remains a challenge, those who apply Doppler
studies to their at-risk patients appreciate its
utility in improving diagnostic precision by allowing
a greater understanding of pathophysiology, and permitting
an insight into therapeutic interventions. As
evidence supports the association of abnormal Doppler
values with poor perinatal outcome, studies will
focus on using Doppler velocimetry to alter treatment
patterns in an effort to decrease perinatal morbidity
and mortality.
Reverse end-diastolic umbilical artery flow can be
seen as early as 11 weeks [116], while differences in
fetal size and amniotic fluid volume may be appreciated
at as early as 9 weeks of gestation [117]; thus,
early ultrasound and continued improvements in amniotic
fluid estimation in twin pregnancies will facilitate
early diagnosis of twin disorders [118, 119].
Continued advances are expected detailing the
pathophysiology of twin pregnancies. Doppler observations
in the fetal circulation of discordant twins
allow differentiation between growth discordance due
to placental insufficiency and twin-to-twin transfusion
[120]; for the latter, continued Doppler investigations
into the venous side of the fetal circulation will
clarify right-sided failure and cardiac function in affected
fetuses [121, 122]. In addition, cordocentesis
studies in monochorionic twins can assess the diagnostic
value of serum erythropoietin, pancuronium
bromide, and hematological and other biochemical
studies in TTS [123±125].
Finally, Doppler sonography may play a role in the
early identification of pregnancies at risk for TTS by
color Doppler identification of communicating vessels.
Less clear is color Doppler's role in supporting surgical
approaches to this disorder by defining the location of
these vessels. Furthermore, the inclusion of Doppler
parameters into the evaluation of patients with TTS
will prove useful in counseling patients, monitoring
disease progression, and determining appropriate interventions.
There is a need for randomized trials to
determine the most effective treatments for TTS.
Conclusion
Doppler velocimetry supplements ultrasound biometry
in multiple pregnancies for detection of the growth-restricted
fetus. Fetal Doppler abnormality may precede
alterations in growth and allow early identification of
the at-risk fetus [32]. Similarly, abnormal velocimetry
may precede other adverse events, such as the development
of fetal hydrops [31] or the development of hypertensive
disorders of pregnancy. Initial reports also suggest
a role in predicting neonatal outcome. This technology
adds to our understanding and knowledge of
the complex hemodynamic changes in the TTS. Finally,
Doppler velocimetry in multiple gestations serves as an
important and accurate indicator of fetal vulnerability,
allowing for appropriate surveillance and intervention
for these at-risk pregnancies.
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