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Why Do I Need A Full Bladder For My Ultrasound Scan?

If you’ve ever gone for an ultrasound scan you’ve probably been told by the sonographer or nurse that you need to have a full bladder in order to carry out the scan. One of the most common questions we get asked is “why do I need a full bladder for my ultrasound scan?”. Don’t worry, there is a reason for this and a very good one.


How Ultrasound Works


Ultrasound was developed many many years ago. It was first used by a man called Karl Dussik for medical reasons in 1942 which he used to try and detect brain tumours in the human skull. An adaptation of ultrasound was also being used by submarines in the navy which is more commonly known now as sonar.


Ultrasound works by emitting high frequency sound waves through the human body and when they hit an object they reflect back thus providing us with an image. These waves travel at different speeds throughout the body and like a submarine, work best in water.


The following scans require a full bladder:

  • Pregnancy scans under 14 weeks
  • Pelvic scans (also known as gynaecological, uterus or ovary scans)
  • Urinary tract (also known as renal, kidney or bladder scans)


Once you are over 14 weeks pregnant, we no longer require you to have a full bladder as the uterus is big enough for us to see everything clearly.



One of the main reasons why you need a full bladder is to avoid your pelvic region being full of gas during the scan. Ultrasound waves don’t travel well through gas which means they won’t be able to produce a clean image of your internal organs. Unfortunately the only way to combat this gas is to ensure the person receiving the ultrasound has a full bladder.


Ultrasound & Water

Ultrasound and water go hand in hand which is why it’s so beneficial for submarines who are constantly submerged in water. This is also the reason why sonographers use gel between your skin and probe when conducting the scan. Ultrasound waves travel much easier through water and fluids than they do through gas and other objects.


Your Bladder Works As A Window

A full bladder allows ultrasound waves to travel through deep into your pelvic region which makes it easier to scan the uterus or other pelvic organs. Try to avoid using the bathroom once you try to fill up your bladder. It’s also recommended that you eat a meal before attending an ultrasound as food will help retain water in your body and slow down liquid being absorbed into your body.



Now that you know the importance of having a full bladder for an ultrasound, be sure to come prepared for your scan to avoid the disappointment of a suboptimal pictures, or having to wait while your bladder fills up to get the best results possible. In some cases, if your bladder isn’t full enough you may be asked to come back another day and to try again. Not every scan requires a full bladder.


Ultrasound Scan

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