Hi Gab
During my ICSIs I think I had 3 or 4 scans - one at the start, one a week later, then another one a couple of days later, and a fourth a couple of days after that, to check the size and number of the follicles, and the thickness of the endometrium. I think it depends how long it takes you to be ready.
As Bella said, it's different at different places. I also have difficulty working the treatment around work, so I try to find out as far in advance when the scans will be as it gives me longer to work out excuses! My clinic does scans very early in the morning, but I still end up being quite late. A couple of the excuses I've used are: picking up DH from the airport and having a carpet fitted / boiler serviced / washing machine fixed /meter read etc, anything where you might need to wait in for a morning - then I work late so I don't have to take any leave.
Wishing you luck and keep positive
Beano