I guess you have to define "extremely rare", and then you would have to know the percentage of women over 45 (for the sake of this discussion) actually actively TTC.
My OB/GYN who is also an RE said the oldest he saw was 47, and he has a lot of experience. (I didn't ask, but I am pretty sure it was NOT IVF).
Furthermore, once I was listening to a radio program and they did mention that every year a (ok, super small number) of women over 50 give birth. So, rare, yes, maybe, but it does happen.
On this board, a woman named "Annie from Finland" wrote in to say she was pg after giving up and not really TTC but still desiring a child. 1st pg. She was 47.
Best wishes to all,