New Yahoo CEO Mayer is pregnant

She told Fortune exclusively that her first child is due in October.

FORTUNE --Marissa Mayer, the Google (GOOG) executive who today was named Yahoo's (YHOO) new chief executive, is pregnant.

Mayer told Fortune exclusively that her first child is due October 7. It's a boy!

"He's super-active," Mayer told me in a phone call tonight, three hours after Yahoo announced her appointment. "He moves around a lot. My doctor says that he takes after his parents."

Career-wise at least, Mayer, 37, has remained in one place for more than a decade. She was Google's 20th employee and its first female engineer, ascending to her most recent post as vice president in charge of local and location services over a 13-year career. That job included overseeing Google Maps, Google Earth and Zagat, a 2011 acquisition that she engineered.

MORE: Marissa Mayer is the new CEO of Yahoo

Mayer's husband is Zachary Bogue, a lawyer who traded practicing law to invest in "big-data startups," she says. Bogue recently launched an investment fund called Data Collective.

Of course, her pregnancy, which Mayer learned of last January, was something to think about when she got the initial call from Jim Citrin, the Spencer Stuart recruiter commissioned by the Yahoo board. "I got the call on Monday, June 18," recalls Mayer, adding that she was "very moved and flattered." Yahoo's huge audience of more than 600 million visitors intrigued her, as did the potential to make the struggling company's products "much more innovative and delightful."

Mayer insists she was "very happy at Google" and "coming into my own" even though Larry Page, after he assumed the Google CEO job from Eric Schmidt last year, slid Mayer out of the CEO's inner circle.

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.

MORE: Andreessen on Marissa Mayer's new role at Yahoo

Asked if she expects Ross Levinsohn, the Yahoo interim CEO who was expected by most people to get the permanent job, to stay at the company, Mayer replies: "I haven't been commenting on my conversations with Ross." She calls Levinsohn "a phenomenal executive."

As for maternity leave, Mayer, who recently joined the board of Walmart (WMT), expects it to be speedy. "I like to stay in the rhythm of things," she says, referring to the CEO job that she is starting tomorrow. "My maternity leave will be a few weeks long and I'll work throughout it."

The Yahoo board did make one concession for its expecting chief executive: The September board meeting, scheduled to be in New York, will be in Yahoo's hometown of Sunnyvale, California.

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