Actresses get pregnant. This has little to do with the charcter she plays on TV, especially if I cannot see it when watching the show. This is true whether she is very young or very old. It is called acting, and it has no bearing on what she does in her private life.
An actress' pregnancy doesn't affect the way I see her acting ability and I don't find myself thinking that she should give up acting or anything along those lines. However, it does make me see her more as a person who has a normal life, like the rest of us.
We live in a time where film technicians use a little technique called "movie magic". Movie magic can use camera angles and wardrobe tricks to conceal an actress' pregnancy. "The New Girl" with Zooey Deschanel was a great example of this. Zooey was ordered to be on bed rest while she was pregnant, so the shows writers gave her the season off and an off camera storyline that fit in with the show.
No, the pregnancy of an actress does not change the way I view her television character. Just like any other working women, an actresses has a job to do regardless of if she is a mother or not. She should not be judged or her television character impacted at all over the fact she was pregnant.