What is a Doppler scan?

What is a Doppler scan?
A Doppler is a form of ultrasound scan that helps to assess your baby’s health. It measures the blood flow in different parts of your baby’s body, such as his umbilical cord, brain and heart. This helps to show whether he’s getting all the oxygen and nutrients he needs via the placenta.

A Doppler scan can be performed at the same time as a normal ultrasound and uses the same equipment. Most ultrasounds have a Doppler function. The person carrying out the scan (sonographer) will put some gel on your tummy and move a hand-held device (transducer) over your skin.

The transducer sends out sound waves, which bounce off the blood flow to your baby’s body via the cord as well as his blood circulation system. This creates an image on a screen showing the sonographer how the blood is flowing. It gives a good idea of how your baby’s doing.

The Doppler scan will take just a few minutes during your regular ultrasound scan. It all happens in real time and your sonographer will analyse the results for you.
Are Doppler scans safe?
As with all ultrasound scans, Doppler scans are safe in trained hands. When carried out by a trained sonographer, doctor or midwife, a Doppler scan helps to give a clear picture of your baby’s health and wellbeing. Used properly, Doppler scans pose no risk to your baby in the second and third trimesters.
Why might I need a Doppler scan?
Your doctor may recommend a Doppler scan if you need extra care during your pregnancy, for example if:

a.   you’re carrying twins or more
b.  your baby is affected by rhesus antibodies
c.   your baby is affected by slapped cheek syndrome (parvovirus)
d.  your baby isn’t growing at a healthy rate
e.  you’ve previously had a small baby
f.   you’ve previously experienced a late miscarriage or suffered the loss of your baby at birth
g.  you have an existing medical condition, such as diabetes or high blood pressure
h.  you have a low or high BMI
i.   you smoke

If your baby is small for dates, a Doppler scan can help to show whether the placenta is working normally.
What does a Doppler scan look for, and why?
In general, Doppler scans look at the blood flow between you and your baby, to check whether he’s getting everything he needs to develop healthily.

Your sonographer will check different areas depending on your personal situation. These Doppler scans are a kind of screening test, so not all hospitals routinely offer them. You’ll generally only be offered Doppler tests if your doctor or midwife has concerns about how your pregnancy is going.

Uterine artery Doppler scans

Uterine arteries are the vessels that carry blood to your womb (uterus). A uterine artery Doppler scan checks that enough blood is reaching your placenta.

Your baby needs plenty of nutrients and oxygen to grow at a healthy rate. Therefore, the walls of your 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 your womb easily. This is called low resistance.

If blood can’t get through to the placenta easily enough, your baby may not get the nutrients and oxygen he needs via the umbilical cord. Factors such as smoking, high blood pressure, hormone levels, and certain medications may increase the resistance in your artery walls.

Umbilical artery Doppler scans

If your baby seems to be growing slowly, is affected by rhesus antibodies, or you’re carrying twins, you may be offered a different type of Doppler. This is called an umbilical artery Doppler, and it looks at the blood flow from your baby, via the umbilical cord, to the placenta. This is a very safe and effective way of finding whether your baby is getting everything he needs from your placenta.

If any issues are found during an umbilical artery Doppler scan, an obstetrician will give you further advice. She may request additional Doppler studies to look at the blood flow in your baby’s brain and his aorta, which is the main artery in his body.

Alternatively, she may request that you visit her a couple of times a week for more umbilical artery Doppler scans. These will check that your baby’s healthy and help you and your doctor to decide the best time and place for you to give birth. Rest assured that even frequent Doppler scans will cause no harm to your baby.

If either scan shows that your baby isn’t getting enough nutrients or oxygen, you may be advised to give birth early. It’s a different picture if you just happen to be carrying a small baby. A small baby with a normal blood flow via the umbilical cord is probably getting all the nutrients he needs.
Should I use a Doppler at home?
It’s possible to hire or buy a portable Doppler machine, also known as a fetal Doppler, to listen to your baby’s heartbeat at home. However, most doctors and midwives advise against using one.

It’s understandable that you’d like to be reassured that all is fine, but it’s best not to set much store by a home Doppler. It may be difficult to find your baby’s heartbeat which could worry you unnecessarily.

Hand-held Dopplers can also be falsely reassuring. It’s very easy to pick up the sound of blood flowing through the placenta or your own vessels and mistake this for your baby’s heartbeat.

Being aware of your baby’s movements and changes in patterns of movement is a far more reliable way of monitoring his health. If you’re at all concerned about a change in your baby’s activity, contact your midwife for advice.
What is a cardiotocograph?
A cardiotocograph (CTG) is a form of Doppler that uses only sound, and doesn’t produce an image. It monitors your baby’s heartbeat and checks that it’s beating at a normal rate. A healthy baby’s heart rate varies from beat to beat and increases when he moves around.

You can ask your midwife to listen to your baby’s heartbeat early on, but this may make you anxious. That’s because your baby’s heartbeat may be hard to find any earlier than 13 weeks.

If you have a healthy pregnancy you won’t need to have a CTG. If you can feel your baby moving regularly during the day, he’s likely to be fine. However, if your baby’s movements slow down, it’s very important that you get in touch with your midwife straight away.
How is a CTG used during labour?
Using a CTG during labour is known as electronic fetal monitoring (EFM).

CTG during labour is used to monitor your baby’s heartbeat and your contractions. If you’ve had a healthy pregnancy and your labour is progressing well, you won’t need CTG. That’s because midwives have other, less invasive ways of monitoring, which should be enough to take care of both you and your baby.

Most maternity units ask that you have a short CTG, of around 30 minutes, when you are admitted in labour. The readings can then be used as a baseline, should the unit’s staff require it later on in your labour.

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