Having an ultrasound scan

An ultrasound uses high frequency sound waves that bounce off solid objects and create a picture on screen. Although it’s lovely to see your baby on a screen (even if the picture is blurry) it’s really done to provide information about her growth and development.

Things your ultrasound can show:

• your baby’s size, which is important for dating the pregnancy and finding out when the baby is due
• the way your baby is lying in the uterus, which may be important at the end of your pregnancy
• whether twins (or more!) are present
• the development of your baby’s organs and bones, including the spine. An ultrasound scan can also show some abnormalities or problems, but it is not always possible to identify them
• where the placenta is lying. In late pregnancy, a low-lying placenta may cause bleeding and block your baby’s way out, so you may need a Caesarean section. See Planning for the birth for more information.

Ultrasound can also be used to find out the exact position of the baby to allow the doctor to carry out other tests such as amniocentesis or CVS.

In the few cases where ultrasound reveals an unexpected problem, you may be referred for further diagnostic tests.

National guidelines say that women should be offered two scans at around 12 and around 20 weeks. The first is known as the ‘dating scan’ because it helps to show how many weeks pregnant you are. The second is a more detailed scan that helps to pick up any problems. In practice, you may find that provision varies across the country. In some areas you may be offered a special ultrasound called a ‘nuchal translucency scan’ (NT) which is done at 11 to 13 weeks, in combination with a blood test, as a screening test for Down’s syndrome. Your midwife will give you information about what is available in your area.

What actually happens?

Depending on how many weeks pregnant you are, you will probably have to fill your bladder before a scan by drinking lots of water. This means your bladder pushes the uterus up and lets the ultrasonographer get a better picture. It’s a bit uncomfortable for you as you may want to go to the toilet, but it is painless.

How it’s done

You lie down on a couch and the ultrasonographer stands or sits next to you. You’ll need to adjust your clothes so that your abdomen (tummy) is uncovered. Cold gel is spread on your abdomen and then a hand-held instrument (called a transducer) which looks a bit like a microphone is rolled over your abdomen. This picks up a picture of everything underneath it and transmits it to a screen.