I have seen conflicting info on this. My letter just says "we may ask you to have a full bladder" but it is their standard scan wording which isn't specific to the 12 week scan.
If you recently had yours, what did they tell you to do? I really don't want to feel uncomfortable with a full bladder if it's not necessary, and then be asked to empty it for the scan, as I would rather avoid using the toilet and exposing myself to more germs ideally :)
Thanks!