1. The role of doppler
ultrasound in 2013
obstetrics
8th December
2. Doppler effect
By Christian Doppler
The apparent variation in frequency of sound waves as the
source of the wave approaches or moves away relative to an
observer
Apparent change in sound level of a train approaches and
then departs a station
This apparent change in sound pitch (Doppler effect) =
frequency shift, and is proportional to speed of movement
3. In clinical application
US beam (with a certain frequency) insonate a
certain blood vessel, the reflected frequency
(= shift) is proportional to the speed of RBCs
that are moving (blood flow velocity)
5. Given that the velocity of flow in a particular
vascular bed is inversely proportional to the
downstream impedance to flow, the
frequency shift therefore denies information
on the downstream impedance to flow of the
vascular bed under study
9. Fetal arterial doppler (UA)
A low impedance circulation with an increased in
the amount of end diastolic flow with advancing
gestation ( increased tertiary stem villi)
UA flow reflects the placental circulation
Decreases that obliterates small muscular arteries
(tertiary stem villi) = progressive decrease in end
diastolic flow until absent - then reverse flow
10. Reverse flow = 70% placental arterial obliteration--> in IUGR
or oligohydramnios
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16. MCA
Most accessible cerebral vessel to US in the
fetus
Carries 80% of cerebral blood flow
Cerebral circulation is a high impedance
Reverse of flow (against UA)
17. In the presence of fetal hypoxaemia
Cerebral redistribution
Brain
sparing
reflex
Increased flow to brain, heart and
adrenals
Reduction in peripheral and placental
circulation
Fetal adaptation to O2 deprivation
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23. Fetal Doppler + IUGR = confirmed by Doppler
Not good for timing
Presence of reversed end diastolic flow
Advanced fetal compromise
For delivery except for extreme prematurity
Preferably by CS
.... < 34w
