An ultrasound scan can be used to monitor an unborn baby, diagnose a condition, or guide a surgeon during certain procedures.
How ultrasound scans work
A small device called an ultrasound probe is used, which gives off high-frequency sound waves. You can’t hear these sound waves, but when they bounce off different parts of the body, they create “echoes” that are picked up by the probe and turned into a moving image. This image is displayed on a monitor while the scan is carried out.
Preparing for an ultrasound scan
Before having some types of ultrasound scan, you may be asked to follow certain instructions to help improve the quality of the images produced. For example, you may be advised to:
- drink water and not go to the toilet until after the scan – this may be needed before a scan of your pelvic area
- avoid eating or drinking for several hours before the scan – this may be needed before a scan of your digestive system, including the liver and gallbladder
Depending on the area of your body being examined, the hospital may ask you to remove some clothing and wear a hospital gown.
In some cases, you may also be given an injection of a harmless substance called a contrast agent before the scan, as this can make the images clearer.
What happens during an ultrasound scan
Most ultrasound scans last between 10 and 20 minutes. A small handheld probe is placed on your skin and moved over the part of your body being examined.
A lubricating gel is put on your skin to allow the probe to move smoothly. This also ensures there’s continuous contact between the probe and the skin.
You shouldn’t feel anything other than the sensor and gel on your skin (which is often cold).
If you’re having a scan of your womb or pelvic area, you may have a full bladder that causes you a little discomfort.
There will be a toilet nearby to empty your bladder once the scan is complete.
After an ultrasound scan
In most cases, there are no after-effects and you can go home soon after the scan is finished.
If a sedative wasn’t used, you can drive, eat, drink and return to your other normal activities straightaway.
If you had an endoscopic ultrasound and were given a sedative to help you relax, you’ll usually be advised to stay in hospital for a few hours until the medication starts to wear off.
You’ll need to arrange for someone to pick you up from the hospital and stay with you for the next 24 hours.
You shouldn’t drive, drink alcohol or operate machinery during this time.
You may be told the results of your scan soon after it’s been carried out, but in most cases the images will need to be analysed and a report will be sent to the doctor who referred you for the scan.
They’ll discuss the results with you a few days later or at your next appointment, if one’s been arranged.
Are there any risks or side effects?
There are no known risks from the sound waves used in an ultrasound scan. Unlike some other scans, such as a CT scan (link), ultrasound scans don’t involve exposure to radiation.
External ultrasound scans don’t have any side effects and are generally painless, although you may experience some discomfort as the probe is pressed over your skin.