The main reasons you would need an early scan are;

1. dating- if you have an irregular cycle, or if you haven't had any sort of cycle since giving birth

2. Prior history of miscarriage/ early bleeding

3. Any indication of possible miscarriage- bleeding or cramping.

Otherwise, you are considered "normal" until proven not to be, and have a scan around 12 weeks, for neuchal fold...Some people elect not to, and have only morphology (spelt wrong I know ) which is at 19-20 weeks.

Congratulations on your pregnancy.