Depends on what kind of blood test you will be taking. If it's a glucose blood test then you have to fast for the minimum 8 hrs before the blood test. Only drink water in the morning before the blood test.
Have you had your antenatal screen done yet? Meaning things like full blood count, hepatitis, etc. If you haven’t, this is probably the antenatal screen. You don’t have to fast for it.
I had a morning appointment and instructions were to not eat or drink after 12am. Only plain water.