What is a Fetal Colour Doppler ?
Let’s start with an example. When standing at railway station, we can always tell by the sound of the whistle that the train is approaching us or moving away. Similarly when filling a bottle/bucket with water, we can tell without looking that its almost full because the sound changes. Now this is known as doppler effect that is source of waves is moving with respect to an observer. Waves emitted by a source travelling towards an observer get compressed. In contrast, waves emitted by a source travelling away from an observer get stretched out. Meaning that the frequency of the waves changes. This is known as doppler effect named after the physicist Christian Doppler. And since we use this principle in our scan, it is known as doppler scan.
Now the colour part. We know that Ultrasound scan uses sound waves of ultrasonic frequency, and human ear cannot hear them. Hence someone thought of light waves(different frequency light wave have different colour). So the colour doppler uses a connected computer to adjust the emitted sound waves into varying colours to produce a final coloured image(red when moving towars and blue when moving away).
In ultrasound scan, sound waves are sent to the fetus and the reflected waves are used to form an image. Blood is a moving fluid. So using the doppler effect with colour, we can have an understanding of the blood flow through the different blood vessels in the fetal heart and the other principal organs in the body.
This is known as colour doppler. This principle is actually used in all the pregnancy scans. However the tradename “colour doppler scan” generally denotes to the scan done later in pregnancy mainly to look for blood flow in the fetus(unborn child) mainly in the umbilical cord, brain of fetus, liver and heart of fetus. Generally blood flow to the womb is also checked.
If you are worried and tired of the constant poking and prodding during pregnancy, a color doppler is a safe and painless procedure. It doesn’t involve any needles and doesn’t require any special preparations for the test.
Who all need “colour doppler scan” ?
It can be used routinely as a part of baby’s surveillance in third trimester, However it is especially recommended for high risk patients:
- Your baby is smaller than expected for his gestational age and may have Fetal Growth Restriction (FGR).
- Your first trimester scans/ blood tests had predicted a higher chance of fetal growth restriction(FGR).
- You are experiencing fewer baby movements.
- You have any bleeding during pregnancy.
- You have an existing medical condition, such as diabetes or high blood pressure.
- You have a low or high BMI.
- You have low amniotic fluid (oligohydramnios).
- You’re carrying twins or more.
- Your blood group is Rhesus negative(Rh neg) and there is chance of baby being affected by it.
- You catch slapped cheek syndrome (human parvovirus B19) in the first 20 weeks of your pregnancy.
- You’ve previously had a small baby.
- You’ve previously experienced a late miscarriage or suffered the loss of your baby at birth.
- You smoke.
What is to be done prior to exam?
Kindly take appointment at least one day prior to exam.
Please come with a comfortably full bladder.
It is helpful to hold off on using any creams or lotions on your belly on the morning of your test. If you have had any previous tests, such as a past ultrasound, bring any medical records that you have.
Kindly turn off your phone/keep it in silent mode before entering the ultrasound room and throughout the examination.
What will happen during the examination?
The scan will be performed in dimly lit room and you would be asked to lie on a flat couch. Clear(perhaps cold) ultrasound gel will then be applied and the ultrasound specialist will commence the exam. To get optimum views of your baby, slight pressure may have to be applied.
The ultrasound specialist will perform a series of measurements to check the growth of the baby.
The ultrasound specialist will check different areas depending on your personal situation. Generally,
the blood flow in four main vessels is checked. These are:
- Uterine artery (mother’s vessels)
- Umbilical artery (from the cord)
- Middle cerebral artery MCA (that supplies the brain)
- Ductus venosus (that supplies the heart)
The time duration varies, but is usually between 15-30 min.
Occasionally the picture quality is poor, this may be due to the position of the baby, your bladder not being full enough or your size. Sometime the baby’s position makes it difficult to complete all the checks in one go. In these situations, you may need to have a repeat scan.
Benefits:
The Doppler exam is very important in the management of IUGR in pregnancy. Firstly, Doppler results will help your doctor decide on pregnancy follow-up and when to schedule your next examination. Secondly, vital organs of the baby can be examined so as to monitor their oxygenation and development rate.
In the event of a pathological diagnosis, Doppler tests also play a big role with regard to delivery and the baby’s life after birth as well as to choice of clinic. A Doppler ultrasound will provide the needed information for a better pregnancy outcome. Moreover, Doppler results will also determine if there is the need for selection of a specialized hospital for delivery, since both doctors and parents will be forewarned as to the possibility of a challenging after-birth condition requiring specialist care.
Are there any risks to having frequent Doppler ultrasound scans?
There are no limitations to the number of times you can take this exam. When IUGR is suspected, a Doppler test is done once a week or fortnightly. However, when there are pathological Doppler findings, the scan will be performed two or three times per week; in special cases, it might be done daily. According to the available evidence, Doppler scans appear to be safe for both the mother and the unborn baby.
Limitations:
Doppler evaluation at particular time assesses the condition of that particular time. Normal doppler values are reassuring, however it does not guarantee normality in future.
There is a range of physiologic factors that can transiently alter the Doppler parameters during the examination. These include fetal breathing, fetal movement, maternal breathing, fetal heart rate etc.
What happens after the examination?
You would usually receive the printed report on the same day.
You can take appointment for any subsequent scans which would then be arranged at the correct time.