If a problem is picked up on the dating scan you will usually be offered further tests and referred on to a more specialist department to find out more about what's going on.
If the screening tests find that your risk for any of the abnormalities tested for is high, you will be offered diagnostic tests such as CVS (chorionic villus sampling) and amniocentesis to find out for sure if there's a problem.
It may not be immediately obvious which parts of your baby you're looking at, but the sonographer will be able to help you work it out.
They will look at the placenta itself and will take note of its position, which may have implications for later in the pregnancy.
A low-lying placenta usually moves up later in the pregnancy but if it doesn't, it can cause problems in labour so they will want to check its movements throughout your pregnancy.
You're under no obligation to have these, and they do usually carry a small risk of miscarriage as they are invasive.
These pregnancy scans pose no risk at all to either you or your baby.