Ultrasound scan

6 min read

What is an ultrasound scan?

An ultrasound scan, sometimes called a sonogram, is a procedure that uses high frequency sound waves to create an image of part of the inside of the body, such as the heart.

As sound waves are used rather than radiation, the procedure is safe. Ultrasound scans are commonly used during pregnancy to produce images of the baby in the womb.

Ultrasound scans can also be used to detect heart problems, examine other parts of the body such as the liver, kidneys and abdomen, or help to guide a surgeon performing some types of

. Read more information about
what an ultrasound scan is used for

What happens during an ultrasound scan?

Most ultrasound scans don’t take long to perform, typically between 15 and 45 minutes. Your ultrasound scan will generally take place in an X-ray department in hospital and be performed either by a doctor, who will provide a diagnostic report, or by a sonographer. A sonographer is a specialist trained in the use of ultrasound, who will provide a descriptive report for the doctor to make a diagnosis.

Before having some types of ultrasound scan, you may be asked to follow certain instructions before the procedure, such as:

  • drink water and not go to the toilet until after the test – this is to fill your bladder and may be needed before a scan of your unborn baby or your pelvic area
  • avoid eating for several hours before the scan – this may be needed before a scan of your abdomen

There are different kinds of ultrasound scans depending on which part of the body is being scanned and why. The three main types are:

  • external ultrasound
  • internal ultrasound
  • endoscopic ultrasound

External ultrasound

An external ultrasound scan is most often used to examine your heart or an unborn baby in your womb. A small handheld device called a transducer is placed onto your skin, and moved over the part of the body being examined.

A lubricating gel is put onto your skin. The gel allows the transducer to move smoothly ensuring there is continuous contact between the sensor and the skin. The transducer is connected to a computer and a monitor. Pulses of ultrasound are sent from a probe in the transducer, through your skin and into your body. They then bounce back from the structures of your body to be displayed as an image on the monitor.

As well as producing still pictures, an ultrasound scan shows movement that can be recorded onto video.

You should not feel anything other than the sensor and gel on your skin (which is often cold). If you are having a scan of your uterus, your full bladder may cause you a little discomfort.

Internal ultrasound

An internal examination allows a doctor to look more closely inside the body at organs such as the prostate gland, ovaries or womb. An ultrasound probe is placed into the vagina or rectum and images are transmitted to a screen. Internal examinations may cause some discomfort but do not usually cause any pain.

Endoscopic ultrasound

Endoscopic ultrasound is where a long, thin, flexible tube called an endoscope is inserted into your body, usually through your mouth, to examine areas such as your stomach, food pipe (oesophagus) or the lymph nodes in your chest.

The endoscope has a light and an ultrasound device on the end. Once it has been inserted into the body, ultrasound waves are used to create images in the same way as an external ultrasound.

You will usually be given painkillers and a sedative to keep you calm as endoscopic ultrasound can be uncomfortable or make you feel sick.

Internal and endoscopic ultrasound is more effective than external ultrasound for examining some organs in close detail. However, because an object enters your body, there is more discomfort and a small risk of side effects, such as internal bleeding.

Other types of scan

Ultrasound waves cannot pass through bone, air or gas. This means they are unable to produce clear and detailed images of some parts of the body, for example the brain, because it is surrounded by bone.

Other methods, such as

barium tests
computerised tomography (CT) scans
magnetic resonance imaging (MRI) scans
can be used to examine parts of your body not suitable for ultrasound scanning.

What is an ultrasound scan used for?

An ultrasound scan can be used in several different ways, such as monitoring an unborn baby, diagnosing a condition or guiding a surgeon during certain procedures.


Ultrasound scans are routine procedure for pregnant women. They produce images of the unborn baby inside the womb, and display them on a monitor.

Most women are offered at least two ultrasound scans during pregnancy:

  • the first scan (at around eight to 14 weeks) can help to determine when the baby is due
  • the second scan (usually between 18 and 20 weeks) checks for structural abnormalities, particularly in the baby's head or spine

However, an ultrasound scan can be done at anytime during pregnancy and causes no harm to the baby.

Diagnosing conditions

Ultrasound scans can help diagnose problems in many parts of your body, including your:

For example, it can help to detect whether a lump in one of these organs is a tumour or a cyst.

Ultrasound may also be used to diagnose problems with your:

  • blood vessels (
  • joints, ligaments and tendons
  • skin
  • eyes

The hip, spine and brain of newborn babies can be scanned for abnormalities but by 18 months old the skull has fully grown and it is no longer possible to use ultrasound on the brain without surgery.

Echocardiogram (ECG)

An ultrasound scan can be used to examine the size, shape and movement of your heart. For example, it can check that the structures of your heart, such as the valves and heart chambers, are working properly and your blood is flowing normally. This type of ultrasound scan is called an echocardiogram (ECG).

ECG can also be used to diagnose heart problems in babies, even before they are born. This is called foetal echocardiography, and is carried out during routine antenatal examinations. Read more about

how congenital heart disease is diagnosed


Ultrasound can be used to guide doctors during certain procedures, such as a

(where a tissue sample is taken for analysis). This is to make sure the surgeon is working in the right area and is often used when diagnosing
breast cancer

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.