Though it's none of our business, it's also not an assumption :)
http://postcards.blogs.fortune.cnn.com/2012/07/16/mayer-yaho...
> Mayer first disclosed to the Yahoo board that she is pregnant in late June, in a meeting with Michael Wolf, a member of the board's four-person CEO search committee. A meeting with the search committee followed, and then Mayer met with the full board last Wednesday. None of the Yahoo directors, she says, revealed any concern about hiring a pregnant chief executive. "They showed their evolved thinking," says Mayer, who got the phone call last Thursday that she was the board's choice to be CEO.