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.
In the few cases where ultrasound reveals an unexpected problem, you may be referred for further diagnostic tests.
How many scans will I have?
National guidelines say that women should be offered at least two scans. The first is known as the ‘dating scan’ because it helps to show how many weeks pregnant you are, it can also check your baby's development. Additionally you may be offered a special ultrasound called a ‘nuchal translucency scan’ (NT) which in combination with a blood test is used to screen for Down’s syndrome. It is offered when you are around 11 to 14 weeks pregnant. In some areas the dating scan and the NT scan will be carried out together.
The second scan is a more detailed scan that helps to pick up any major structural problems and is offered when you are around 18-21 weeks pregnant. In practice, you may find that the timing varies across the country. Your midwife will give you information about what is available in your area.
In the few cases where ultrasound reveals an unexpected problem, you may be referred for further diagnostic tests such as amniocentesis or chorionic villus sampling (CVS). Ultrasound can also be used to find out the exact position of the baby to allow the doctor to carry out these tests.
You should remember that just because nothing unusual is seen on the scan does not mean that your baby will have no problems or anomalies. There are things that the ultrasound scan cannot pick up.
The ultrasound scan you have at 18–21 weeks is looking for common abnormalities and not to identify the sex of your baby.
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.
For further information on screening tests during pregnancy go to www.nsd.scot.nhs.uk
Further information on screening tests offered during pregnancy can be found in the following leaflets available from your midwife:
Pregnancy screening identifies mother and babies who may have rare but serious conditions. Most mothers and babies screened will not have any of the conditions but, for the small number that do, the benefits of screening are enormous. Early treatment can improve their health and prevent severe disability or even death. There are two types of test:
- Screening tests are offered to all pregnant women to assess the chance of you or your baby having a particular health problem or disability
- Diagnostic tests are follow-on tests carried out to find out whether your baby does have a particular condition. They do not provide a definite diagnosis but help you and your midwife decide whether you need further tests to make that diagnosis.
While screening offers a good way to assess how likely it is that your baby has a condition or health problem, it may not detect all problems. If you do not want to be screened for any (or all) of the conditions, please talk this through with your midwife or doctor.
Points to remember
Ask for a picture to take away with you. Some units make a charge or ask for a donation for this.
Ask about anything that is worrying you.
If you don’t want a scan, your decision will be respected.