Yeah Gates started wearing the doctor's jacket to help hide her bump in season 4 - she wasn't pregnant when she left the first time. Pulaski was fun but I'd have been happier if Crusher had stayed and Pulaski had been brought in as a scientist or chief engineer.
Grace wasn't treated terribly well either and I think her departure was a result of a combination of events including a behind the scenes sexual assault (I'm pretty sure it wasn't GR but she remained tight-lipped about the identity as far as I'm aware) and health issues she was having from drinking too much and taking diet pills. The character would have made a decent recurring guest star but as the principle female lead they piled too much into the early scripts about her and Kirk's mutual attraction so it didn't give them enough wriggle room when it came to his romancing the female alien of the week.
It's more disappointing that she and Majel weren't given more to do in the later movies, which ties directly into them being left out of the recent reboot.