Officially you can get pregnant immediately. I remember my dr warning me when it was removed. So yes, you 'can' start TTC immediately. That is no guarantee that *your* cycle will be perfectly normal straight away, though.

I would suggest going to see your GP a few months before you are ready to TTC, have a chat about preparing to TTC. Certain things, like immunisations, should be given we'll before starting. And there might be other tests and health checks your go thinks is appropriate. Then you can book an appt for removal of the Mirena when you are ready to actually start TTC.