I think they look for a few things, est is defo a big one.
I had bt's ever 2 days with antagonist cycles. And 2-3 scans also.
I loved having scans, not the actual scan part (lol) but seeing what's going on inside you is amazing! It's the same when they show you the embie before transfer... now how many people who can conceive naturally can say they have seen that!?!? 0!!