A Doppler is an ultrasound scan that helps assess the baby's growth and blood flow to different parts of the baby's body including the umbilical cord, brain, and heart. This helps to study whether sufficient oxygen and nutrients that the child needs are being supplied via the placenta.
Normal blood flow indicates a healthy fetus and any abnormality in the flow of the blood indicates that the fetus is under stress. Doppler scan is performed usually during the third trimester. In some cases (like high-risk pregnancies) more than one Doppler scan will be asked by the doctor.
Are Doppler scans safe?
As with all ultrasound scans, Doppler scans are safe when performed by a certified fetal medicine specialist.
Why is a Doppler scan required?
The doctor may recommend a Doppler scan in case:
- The patient is carrying 2 babies or more which is considered as high-risk, as there are several possible complications such as growth restriction, TTTS, cord entanglement etc.
- The baby is affected by rhesus antibodies
- The baby isn't growing at a healthy rate
- The patient previously had a small baby
- The patient previously experienced a late miscarriage or suffered the loss of ababy at birth
- The patient has an existing medical condition, such as diabetes or high blood pressure
- The patient has a low or high BMI
- The patient is a smoker
If the baby is not growing at a healthy, normal rate, a Doppler scan can help to show whether the placenta is working normally.
Some of the other conditions for which the doctors recommend a Doppler scan are:
To check the ‘low resistance’ property of the umbilical arteries that enables easy flow of blood through blood vessels. Uterine arteries are the vessels that carry blood to the womb (uterus). A uterine artery Doppler scan checks that enough blood is reaching the placenta.
The baby needs plenty of nutrients and oxygen to grow at a healthy rate. Therefore, the walls of the uterine arteries should be stretchy, to allow as much blood through as possible. In pregnancy, these normally small arteries increase in size to allow more blood to reach the womb easily. This is called low resistance. Lifestyle factors like smoking, intake of alcohol, intake of certain medicines, etc. will increase the resistance of arteries thereby affecting the flow of blood.
To check whether Rh sensitization has occurred. Blood flow through a blood vessel in the brain can be used to check the health of the fetus.
Other understanding that can be gained from a Fetal Doppler scan:
- It helps confirm the fetal heartbeat
- Status of the umbilical cord which transports oxygen and nutrients from the mother to the fetus, which in turn sends back blood devoid of nutrients and oxygen.
- Status of the placenta that transports all the nutrients needed for the baby and also helps eliminate wastes, provide oxygen, take out carbon dioxide, protect the baby from infections, and secrete hormones required during pregnancy.
- General development - The scan can tell how the baby is developing and the growth in terms of length and weight.
- The health of the mother- A Doppler scan can also help determine if there are any issues or complications like clots or cysts in the mother that can cause problems before or during labor.
What does a Doppler scan look for, and why?
A Doppler test during pregnancy can provide details about the blood circulation in the brain, kidneys, heart, umbilical cord, placenta as well as in uterus. It helps confirm the fetal heartbeat
- Uterine artery Doppler scan: Uterine arteries are blood vessels that take blood to the uterus. Normally these arteries are small in size. But in the course of pregnancy, these arteries increase in size (stretches) to provide less resistance and thus allow more blood to flow through them. The Doppler scan in this area helps to check whether enough blood is reaching the womb.
- Umbilical artery Doppler scan: In the umbilical artery Doppler scan, the blood flow from the baby through the umbilical cord towards the placenta is checked. This scan helps to make sure the baby is getting everything he needs from the mother’s placenta. The umbilical artery Doppler scan is performed if the mother is carrying more than one baby or if the growth rate of the baby is less for the gestational period or if the baby is affected by rhesus antibodies
- Middle cerebral artery Doppler scan (MCA Doppler scan): If some issues are detected during the umbilical artery Doppler scan, an MCA Doppler scan is performed to check the blood flow in the baby’s brain.
- Ductus venosus Doppler scan: This scan is done if the first result of any of the above scans shows issues. Here, the blood vessel which carries well-oxygenated blood from the umbilical vein to the heart of the baby is assessed to evaluate the volume of blood reaching the baby
How does the Doppler test work?
A Doppler ultrasound test is painless and non-invasive. It uses reflected sound waves to see how blood flows through a blood vessel. The sound waves bounce off solid objects, including blood cells as they move, giving an accurate picture of their speed. The movement of blood cells causes a change in the pitch of the reflected sound waves. This is called the Doppler effect. If there is no blood flow, the pitch does not change.
From this can be calculated the rate of blood flow moving through the umbilical cord between baby and placenta. Functionality and health of the placenta are thereby checked, as also that of other major blood vessels. Blood clots, blocked arteries, or reduced blood flow can all be identified, as well as the risk of pre-eclampsia.
What is the difference between a normal ultrasound and a Doppler ultrasound?
A normal ultrasound will not show the rate of blood flow, but a Doppler scan will show the rate of the blood flow and blood pressure in the placenta, umbilical cord, brain, and heart of the baby.
Normal ultrasound scans show only the image of the baby but Doppler can help hear the heartbeat and the amount of oxygen and nutrients the baby gets by accessing the blood flow rate.