Hi, back in May/2011 someone questioned the same thing. Here is the link (I saved it because is very helpful to know!)
http://www.mamapedia.com/questions/11448950971162558465
I copied the answer of a former hiring manager (JessicaWessica):
I'm speaking as a former hiring manager here. Absolutely do not bring up your pregnancy. If they lay out duties that are required for the job that you would be unable to perform due to the pregnancy then you would have to reply, "No, not at the moment, but I could do them by such-and-such date." I was once forced to interview a college friend that I knew was pregnant and she was showing although she had not officially announced or confirmed her pregnancy to anyone. I had to tell her ahead of time that "if" she were pregnant to please not tell me because of the laws about discrimination. And during the interview I had to ask her if she would be able to stand on her feet for 8 hour shifts, climb ladders, carry heavy stock in excess of 50 pounds, etc. Those were required questions because of the position she was applying for. And she could not perform those duties so I couldn't hire her. But if she had discussed her pregnancy in that interview or if I had openly said, "So you ARE pregnant, right Missy?" I would have been forced to hire her.
Just don't do it. Not prior to the interview and not during it either. They're not even allowed to comment on the size of your belly and ask if you're pregnant during an interview even if it's obvious. If you bring it up, it's very bad form for you to do that. You would put them in a really bad legal position of having to acknowledge the pregnancy and then if they choose not to hire you for other legitimate reasons they'll still be opened up to possible lawsuits for discrimination. They can't even ask you if you have existing children at home to care for. They ought to trust that you'll have child care lined up.
If they do ask, though, and openly acknowledge your pregnancy and how late into it you are then reassure them of the childcare you have lined up already. But it would be illegal for them to do that.