Screening Tests in Pregnancy – 20 week scan


Early in your pregnancy you will be asked if you want to have the 20 week scan. This may also be called the ‘anomaly scan‘ or the ‘mid pregnancy scan‘. This is usually a happy and exciting time for a couple. One in which you get to see your baby. However please remember the purpose of the scan.

What happens during this screening test?

You will be taken into a room with a sonographer. You are usually allowed to bring along one adult. It is usually advised where possible not to bring children. There are a couple of reasons for this. Firstly the sonographer need to be able to concentrate. Secondly, if there is anything that needs discussing after then you need to be able to concentrate.

The room will be dark and you will be asked to lie on a couch with your pregnant bump exposed. The sonographer will put some cold jelly on your belly and then proceed to scan. The scan usually takes about 30 minutes. The sonographer will usually be quiet during this time and discuss the scan after he/she has finished.

What is the scan for?

This scan, if accepted will take place between 18+0 weeks and 20+6 weeks of pregnancy. This is the optimum time for looking at the physical structures in an unborn baby. Earlier and the baby has not developed enough to look at all the structures. Later and it becomes more difficult to see everything as the baby gets bigger with less room.

The purpose of this scan is to look for abnormalities. A scan can detect some abnormalities but not all. Hopefully and more than likely you will be told that there appears to be no abnormalities seen via scan. If this is the case you will return to your normal antenatal care. This on the whole is reassuring but does not exclude all abnormalities. You are not usually offered any more scans in your pregnancy unless a pregnancy problem arises or you enter a research project.

Some units will tell you the sex of the baby, some will not. Sometimes it is impossible to see.

More worryingly, you may be told that there is a problem.

Why would you want to know if there is a problem?

Identifying a problem, although terrifying allows us to plan, advise and assist. Some problems may be minor and no action required. Some problems may need monitoring to ensure it doesn’t get worse. Some problems resolve during pregnancy, some resolve soon after birth. Some are more complex and although identified it is hard to give a prognosis for the child. Some problems may require the baby to have surgery soon after birth.

Unfortunately some problems may mean that the baby will not survive. If as a family you know what to expect and healthcare providers know what to expect. Measures can be put in place to make sure the baby is best cared for. You can learn about the problem. You can talk to others about the problem.

If a problem is found, what happens next depends on the extent of the problem. You may be referred to a Fetal Medicine Unit. At the Fetal Medicine Unit your baby will be scanned again and the specialist obstetrician will offer his/her explanation on what they have found. They will discuss options on what to do next and offer full support with any decision. If the problem is severely life limiting or fatal for the baby you will be offered a termination.

Do I have to have the scan?

No, its your choice.


More information and support.

Public Health England – Screening Tests for You and Your Baby

Antenatal Results and Choices – Scans

Fetal Anomaly Screening Programme – Handbook



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