There are many Catholics who use birth control, have abortions, have artificial insemination performed on them. All of which are considered WRONG per Catholic doctrine. Just because Catholics DO something doesn't mean the church has to accept it and say its ok.
That I know and understand. But the way you made it sound was that even the doctor was violating a belief (creating life artificially) that *ALL* Catholics believe. I highly doubt this doctor follows that same belief if he's a fertility specialist.