Purpose of screening

All pregnant women are offered a detailed ultrasound scan between 18 weeks and 20 weeks 6 days of pregnancy, and it is commonly called the 20-week scan. It is also sometimes referred to as the mid-pregnancy or anomaly scan.

The scan will look in detail at your baby’s bones, heart, brain, spinal cord, face, kidneys and abdomen.

In most cases the scan will show that your baby appears to be developing as expected but sometimes a condition is found or suspected. Some things can be seen more clearly than others. For example, some babies have a condition called open spina bifida, which affects the spinal cord.

The scan checks the physical development of your baby. It specifically looks for 11 different conditions in your baby, so it cannot find everything that might be wrong. The 11 conditions screened for are listed below and more information can be found about them under the fetal conditions section of this website:

Spina bifida can usually be seen clearly on a scan and of those babies who have this condition, around 9 out of 10 (90%) will be detected.

Some of the other conditions, such as heart defects, are more difficult to see. The scan will find about half (50%) of those babies who have heart defects.

Some of the conditions that can be seen on the scan will mean the baby may need treatment or surgery after it is born, for example cleft lip. In a small number of cases some very serious conditions are found. For example, the baby’s brain, kidneys, internal organs or bones may not have developed properly. In some very serious rare cases, where no treatment is possible, the baby will die soon after it is born or during pregnancy.

There is more detailed information about the main conditions that are looked for during this scan on NHS.UK. 

About your 20-week screening scan

Most scans are carried out by specially trained staff called sonographers.

In order for the sonographer to get good images of your baby, the scan is carried out in a dimly lit room.

1. You will be asked to lie on a couch.
2. You will then be asked to raise your top to your chest and lower your skirt or trousers to your hips.
3. Tissue paper will be tucked around your clothing to protect it from the ultrasound gel, which will then be put on your tummy.
4. The sonographer then passes a hand-held probe over your skin to examine the baby’s body. The gel makes sure there is good contact between the probe and your skin.

Having the scan does not hurt but the sonographer may need to apply slight pressure to get the best views of your baby. This might be uncomfortable. A black and white picture of your baby will then be seen on the ultrasound screen. During the examination, sonographers need to keep the screen in a position that gives them a good view of your baby. The screen may be directly facing them or at an angle.

The appointment usually takes around 30 minutes.

You may need to have a full bladder when you come for the appointment. The doctor or midwife looking after you will let you know before you come. If you are not sure, you can contact them and ask.

You may like someone to come with you to the scan appointment. Most hospitals do not allow children to attend scans as childcare is not usually available. Please ask your hospital about this before your appointment.

Sometimes it is difficult to get good views of a baby. This does not mean there is anything to worry about. If this happens, you will be offered one further scan by 23 weeks of pregnancy. Very occasionally this second scan cannot be completed, for example because:

• a baby is lying in an awkward position
• you are above average weight

In this case you will not be offered another screening scan but you will offered an all over physical examination for your baby after birth.

Safety of the test

There are no known risks to your baby or the mother from having an ultrasound scan but it is important that you consider carefully whether or not to have the 20-week scan. The scan can provide information that may mean you have to make further, important decisions. For example, you may be offered further tests that have a risk of miscarriage.

Screening is your choice

You do not have to have the scan. Some people want to find out if their baby has one of the 11 conditions and some do not.

Not having the test

If you choose not to have the scan you can still have all other parts of your routine antenatal care.

Possible results

Most scans show that babies seem to be developing as expected, and none of the 11 conditions are found.

If one of the conditions is found or suspected, the sonographer may ask for a second opinion from another member of staff.

Scans cannot find all conditions. There is always a chance that a baby may be born with a health issue that scans could not have identified.

Further tests

You might be offered another test to find out for certain if your baby has one of the conditions.

If you are offered further tests, you will be given more information about them so that you can decide whether or not you want to have them. You will be able to discuss this with your midwife or consultant. If necessary, you will be referred to a fetal medicine specialist, possibly in another hospital.

Getting my results

The sonographer will be able to tell you the results of the scan at the time.