Doppler Ultrasound in Pregnancy

DOPPLER ULTRASOUND in Pregnancy
Dr. Mohammed Abdalla
Egypt, Doimat Hospital

Doppler History
First use of Doppler ultrasonography to study flow velocity in the fetal umbilical artery was reported in 1977

Doppler History
• Fitzgerald & Drumm. Umbilical artery studies 1977 BMJ
• Eik-Nes et al. Fetal aortic velocimetry: Dupplexscanner 1980 Lancet
• Campbell et al. Utero-placental circulation: Dupplex scanner 1983 Lancet
• Wladimiroff et al. MCA/UA PI ratio 1987 OG
Kiserud et al. Ductus venosus velocimetry 1991 Lancet

Basic principals
Echoes from stationary tissues are the same from pulse to pulse.
Echoes from moving objects exhibit slight differences in the time for the signal to be returned to the receiver.

These differences can measured as phase shift from which the Doppler frequency is obtained.

T1: time of omitted signal.
T2: time of returned signal.
T2 - T1 = time difference or phase shift.
from phase shift the Doppler frequency is obtained.
AS TIME DIFFERENCE DECREASE THE DOPPLER FREQUENCY INCREASE.

Basic principals
The time difference or phase shift are then proceeded to produce either colorflow display or a Doppler sonogram

Basic principals
• 'Doppler frequency' is obtained by measuring the time difference for the signal to be returned when reflected from moving scatterers.
• Doppler frequency increase if:
1. flow velocity increased.
2. beam is more aligned to the direction of flow.
3. higher transducer frequency is used.

Factors affecting doppler frequency
(the angle q between the beam and the direction of the flow becomes smaller). This is of the utmost importance in the use of Doppler ultrasound.

(the angle q between the beam and the direction of the flow becomes smaller). This is of the utmost importance in the use of Doppler ultrasound.
beam (A) is more aligned than (B)
The beam/flow angle at (C) is almost 90° and the
The flow at (D) is away from the beam and there

Aliasing
If a second pulse is sent before the first is received, the receiver cannot discriminated between the reflected signal from both pulses and aliasing occur.

Aliasing
So to eliminate aliasing The pulse repetition frequency or scale is set appropriately for the flow velocities.

Basic principals
The volume flow in the UAs increases with advancing gestation. The higher vascular impedance detected in the first trimester gradually decreases. It is attributed to growth of placental unit and increase in the number of the functioning vacular channels.

Uses
• plays a vital role in the diagnosis of fetal cardiac defects.
• assessment of the hemodynamic responses to fetal hypoxia and anemia.
• diagnosis of other non-cardiac malformations.

Anatomy
• Blood supply provided by the ovarian and uterine arteries
• Uterine Ateries: main branches of the internal iliac arteries
• Uterine Ateries: Ascend through the lateral wall and anastomose with the ovarian arteries

Anatomy
• Acurate Arteries: Run Circumferentially around the uterus
• Uterus: Blood supply to anterior and posterior walls provided by the Arcuate arteries
• Radial Arteries: Extend from the arcuate arteries and enter the endometrium
• Spiral Arteries: connect the maternal circulation to the endometrium
• Responsible for a 10 fold increase in blood flow

Anatomy
• Conversion of small muscular spiral arteries into large vascular channels transforms the uteroplacental circulation into a low-resistance-to-flow system. These have dilated and tortuous lumen, a complete absence of muscular and elastic tissue, no continuous endothelial lining.

Umbilical artery doppler

Umbilical artery
UMBILICAL ARTERY FLOW
characteristic saw-tooth appearance of arterial flow in one direction and continuous umbilical venous blood flow in the other.

Umbilical artery
Benefit of Umbilicial Artery Evaluation
Less experienced operators can achieve highly reproducible results with simple, inexpensive continuous-wave equipment.

Umbilical artery
The 40% of the combined fetal ventricular output is directed to the placenta by two umbilicial arteries. The assessment of umbilical blood flow provided information on blood perfusion of the fetoplacental unit.

Umbilical artery
• With advancing gestation, umbilical arterial Doppler waveforms demostrate a progressive rise in the end-diastolic velocity and a decrease in the pulsatility index.

Middle cerebral artery doppler

The possible Doppler velocimetry sites
Middle cerebral artery
Using color flow imaging, the middle cerebral artery can be seen as a major lateral branch of the circle of Willis, running anterolaterally at the borderline between the anterior and the middle cerebral fossae

Middle cerebral artery
The blood velocity increases with advancing gestation, and this increase is significantly associated with the decrease in PI

Middle cerebral artery
An early stage in fetal adaptation to hypoxmeia - central redistribution of blood flow (brain-sparing reflex)
increased blood flow to protect the brain, heart, and adrenals
reduced flow to the peripheral and placental circulations

Doppler wave form of early stage of fetal hypoxemia
increase end-diastolic flow in the middle cerebral artery (lower MCA pulsatility index or resistance index)
Average of both MCAs must be calculated for more precise result

Middle Cerebral Artery
Flow velocity waveform in the fetal middle cerebral artery in a severely anemic fetus at 22 weeks (left) and in a normal fetus (right). In fetal anemia, blood velocity is increased

Middle Cerebral Artery
When the fetus is hypoxic, the cerebra arteries tend to become dilated in order to preserve the blood flow to the brain and The systolic to diastolic (A/B) ratio will decrease (due to an increase in diastolic flow)

Doppler ultrasound for the fetal assessment in high-rish pregnancies
(Cochrane Review). In: The Cochrane Library,, 1999. Neilson JP and Alfirevic Z
11 Studies Included In Analysis
• Trudinger et all 1987
• McParland et all 1988
•Tyrrell et al 1990
•Hofmeyer et all 1991
•Newham et all 1991
•Burke et al 1992
•Almstrom et al 1992
•Biljan et al 1992
•Johnstone et all 1993
•Pattison et al 1994
•Nienhuis et al 1997

Doppler ultrsound for the fetal assessment in the high-risk pegnancies
Meta analysis
• Nearly 7000 patients were included
• The trials compared no Doppler ultrasound to Doppler ultrasound in high-risk pregnancy (hypertension or presumed impaired fetal growth)

Doppler ultrasound for the fetal assessment in high-risk pregnancies
Main results
• A reduction in perinatal deaths.
• Fewer inductions of labour.
• Fewer admissions to hospital.
• no report of adverse effects.
• No difference was found for fetal distress in labour.
• No difference in casesaren delivery.

Biophysical profile for fetal assessments in high risk pregnancies
• When compared with conventional fetal monitoring (usually cardiotocography) biophysical profile testing showed no obvious effect (either beneficial or deleterious) on pregnancy outcome. There was an increase in the number of inductions of labour following biophysical profile in the trial.
Alfirevic A, Neilson JP. Biophysical profile for fetal assessment in the high risk pregnancies (Cochrane Review). In: The Cochrane Library, 1995.

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