During pregnancy, you can have screening tests to find out whether your unborn baby has a congenital disorder or any physical abnormalities. This is called prenatal screening. There are two types of screening tests:

1. prenatal screening for Down syndrome, Edwards’ syndrome and Patau's      syndrome, and
2. screening for physical abnormalities (anomaly scan).

It’s entirely up to you to decide whether or not you want to take these screening tests. This leaflet contains further details about the 20-week anomaly scan.
There is also a (printable) document about the prenatal screening for Down syndrome, Edwards’ syndrome and Patau's syndrome.