Congratulations on the offer! Your pregnancy shouldn't affect your offer of employment, but it might. Generally, unless you think you'll need special accommodations, I'd recommend keeping private information to yourself.

It shouldn't affect an offer of employment. If it does, they won't come right out and say your pregnancy is the reason, they would just go with something vague, like, "We decided to go in a different direction."

Not being a woman and never having had a child, I am not sure what the unwritten rules are when it comes to divulging pregnancy to a potential employer.