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Section 5 - Ultrasound scans in pregnancy


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This section explains the two ultrasound screening tests you will be offered during pregnancy.

You can choose whether or not to have these tests.

It explains:

  • what the tests are
  • why they are carried out, and
  • when they are done.

The scan is a way of checking that your baby appears to be developing as expected.

This means it may show up unexpected findings that would then need to be checked by other tests. A scan cannot find all conditions screened for.

This animation gives information on the screening tests you will be offered during pregnancy for you and your baby.

What is an ultrasound scan?

An ultrasound machine uses sound waves to create an image on a computer screen. The person who does the scan is called a sonographer. The sonographer will explain to you what they are doing and what they are looking for.

How is the scan arranged?

If you decide you would like to have a scan, your midwife will tell you where it can be done and will arrange the appointment for you. If you have been given an appointment and then decide you do not want a scan, please tell your midwife and cancel the appointment.

How is the scan done?

You will be asked to lie on your back to have the scan. You do not need to wear any specific clothing for the scans. However, you will be asked to raise your upper clothes to your chest and lower your skirt or trousers to your hips.

Gel is spread on your lower abdomen so that a device called a transducer can be passed backwards and forwards over your abdomen. The sonographer may need to press on your abdomen with the transducer to see your baby properly.

Ultrasound waves do not pass through air, so the gel makes sure there is good contact between your skin and the transducer. Your clothing will be protected from the gel with tissue paper.

The transducer passes sound waves through your abdomen into the womb. The sound waves bounce back off your baby and are translated into an image on a screen. The sonographer will get a clearer image of your baby if your bladder is not completely empty when you have your scan.

Please try not to pass urine for about an hour before your appointment. For the sonographer to see your baby clearly on the screen, the scan is carried out in a dimly lit room. Scanning involves a lot of concentration, so the room is also kept quiet. The sonographer will explain to you what they are doing and what they are looking for.

Are scans safe?

As far as we know, the early pregnancy dating scan and the fetal anomaly scan we offer are safe for mother and baby.


What are early pregnancy dating and fetal anomaly scans?

Both of these scans can detect unexpected findings before your baby is born.

Finding this out before the birth can help you and your partner prepare yourselves. Sometimes it can help plan treatment for after your baby is born. Sometimes when women find out that there are unexpected findings, they may want to consider ending the pregnancy.

What are the disadvantages of having these scans?

Having the scans may make you anxious, especially if there is an unexpected finding. If you prefer not to know, you need to think carefully whether you should have the scans. You should discuss your concerns with your midwife.


How do I get the results of these scans?

The sonographer will tell you the results of your scan at the end of the examination.

Can I bring family or friends with me when I have the scan?

Most babies are healthy, but because the scans can show unexpected findings you may want to ask your partner or one adult who can support you to come with you to your scan.  It is best not to bring children to the appointment.

They can distract you and the sonographer during the scan. If unexpected findings are found on the scan, the sonographer will tell you about them, and this is not a suitable situation for children.

Can I have a picture of my baby?

It is sometimes possible to buy pictures of your baby taken during the scan. Please tell the sonographer if you would like to do this before the scan starts.

The sonographer will obtain the best picture of your baby within the appointment time. Video recording or the use of mobile phones within the ultrasound room and during the scan is not allowed.

The early pregnancy dating scan

You will be offered an early pregnancy dating scan and screening for Down's syndrome, Edwards' syndrome and Patau's syndrome at 11 to 14 weeks. 


How long will my scan take?

The early pregnancy dating scan takes about 10 to 20 minutes.

The scan is done to:

  • check your baby’s heartbeat
  • find out if you are carrying more than one baby (if this is the case you will need extra antenatal care, and it is important to know if your babies are sharing the same placenta)
  • measure your baby to check how pregnant you are and the date your baby is due (this is especially important if you are thinking of having more screening tests)
  • measure the nuchal translucency (the small collection of fluid at the back of your baby’s neck), if you have asked for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome screening, and
  • check your baby’s development (your baby’s development is not very clear at this early stage, but sometimes serious conditions can be detected).

Will I need another early pregnancy dating scan?

Sometimes your baby cannot be seen clearly using an abdominal transducer, so the sonographer may suggest you have an internal scan. This is called a transvaginal scan, and it can give a more detailed picture. You will be asked to empty your bladder before this scan.

A small transducer is inserted into your vagina, similar to having a tampon inserted. A vaginal ultrasound scan is not usually painful. The sonographer will explain about the scan and ask for your agreement to do it. If you do not want to have an internal scan, please tell the sonographer.

You will be offered an appointment for another abdominal scan.

Fetal anomaly scan

This scan is offered at 18 to 20 weeks of pregnancy. 


How long will my scan take?

The fetal anomaly scan usually takes about 15 to 30 minutes.

The scan is done to:

  • check your baby’s physical development
  • help detect structural changes (also called anomalies) such as spina bifida, kidney conditions, or heart conditions
  • check the amount of fluid around your baby in the womb, and
  •  look at the position of the placenta

Looking for the sex of your baby is not part of the scan and is not 100% accurate.

If you want to know the sex of the baby and the sonographer can see it, they will tell you at the time of the scan. They will not write it down.

Will I need another fetal anomaly scan?

The sonographer will use an all-Wales agreed checklist to look for certain conditions (such as spina bifida) and at structures (such as the heart). The sonographer has to concentrate very hard during the scan, so please make sure you and the person supporting you do not distract them.

Sometimes it is not possible to see everything on the list during your scan.

This can be because:

  • your baby was lying in a position which made the examination difficult
  • you are above average weight for your height and this made looking at your baby difficult as the images were not clear.

If this happens, you will be given another appointment to come back for one more scan to see if the sonographer can complete the checklist. It is not always possible for the sonographer to complete the list, even on the second appointment.

What is the scan able to find?

A scan can show some unexpected findings with your baby’s development but not all. Some may develop after 20 weeks and some may not show up on the scan. This is why, in a small number of cases, babies are born with undiagnosed conditions. Table 1 has a list of some examples of conditions. The right-hand column shows how likely it is that a fetal anomaly scan could identify each condition.

This list does not include all conditions that may be seen. Some conditions may be caused by your baby having a chromosome change which affects the way your baby develops. If a chromosome change is suspected, you may be offered an amniocentesis. You can find information on this test in section 7.

Table 1

The condition

The chance of the condition being seen on a fetal anomaly scan at 18 to 20 weeks

Spina bifida (skin or bone not covering the spinal cord)

Spina bifida is a fault in the development of the spine and spinal cord which leaves a gap in the spine.

The spinal cord connects all parts of the body and brain



Major heart condition, for example, tetralogy of fallot

Tetralogy of fallot is a serious heart condition where the heart has not developed in the same way as a normal heart in the womb. This condition will need surgery, usually the first year after birth



Autistic spectrum disorders (autism)

Autism cannot be picked on a scan as there is no structural abnormality


Data from: Welsh Congenital Anomaly Register and Information Service (CARIS)(Accessed 12/01/21)

What will happen if an unexpected finding is suspected during the scan?

If the sonographer detects an unexpected finding, they will tell you about it and you will be able to talk to the midwives or hospital doctor (obstetrician) in your antenatal clinic. Receiving unexpected news can be distressing. We recommend that your partner or one adult only comes with you to the scan appointment.

Sometimes it is not possible, at the first fetal anomaly scan, for the sonographer to tell definitely what the unexpected finding is. You might be offered another scan in a different department or with a specialist dealing with the type of condition your baby is suspected of having.

Invasive tests following a fetal anomaly scan

You might also be offered another test, such as amniocentesis (see section 7). You will be given more information on any other tests by your midwife or your hospital doctor (obstetrician).

What will happen if a definite anomaly is found?

Finding out that your baby may have a condition before the birth can help you and your partner prepare yourselves. Information about the type of condition can be used to prepare for how, when and where your baby is delivered.

Your baby may need to be born in a different hospital that can provide the specialised staff and care that your baby may need. A very small number of conditions can be treated before your baby is born. If the condition is serious, you may decide to continue with your pregnancy or consider ending your pregnancy.

These are difficult decisions and you will be given time, information and support to help you make a decision that is right for you. Finding out that your unborn baby has a condition is distressing and deciding what to do is hard.

Most women want and need some support. This might come from your partner, family or friends or from the health professionals who are caring for you. You can choose to bring your partner or one adult only to hospital appointments with you.