Do I have to book time off for scans?

[RockingLobstering]

Just that really. Had a lot of time off for hyperemisis recently.
Scan is in 2 weeks.

All maternity appointments are protected so your workplace has to give you time off with no penalties.

Yes - you should give your employer reasonable notice wherever possible but you don't need to book leave. You are entitled to time for antenatal appointments.

You're entitled to time off but they can ask for proof

As others have said, you have to tell them you'll be taking off, but it's not annual leave or anything and that time should be paid.