“Don’t leave before you leave.”

Sheryl Sandberg’s guest blog on Fortune Postcards in October 2009 discussed how she noticed women were “leaving” the workforce-whether they were making official exits or just checking out mentally– before they needed to leave to have children. Well Marissa Mayer must have read it (more likely she discussed it with Sheryl since they are known as women who support one another in the Valley).

Yesterday’s announcement that Marissa Mayer would take over struggling titan Yahoo! was a great moment. Yahoo’s choice in Mayer shows a commitment to women and to quality of product. Mayer is a competent leader, product manager, and engineer-and more importantly, she’s willing to take a big risk to potentially lead one of the greatest turnarounds in tech history. If she can make it happen.

For me, as a young woman at the beginning of my career in the digital space, seeing Mayer get to the top of a digital company that needs a turnaround was gratifying. But even more interesting and profound comes the news that Mayer is pregnant-that she will be delivering her child in less than three months, and that the board at Yahoo knew this all along.

One Small Step for a Woman, One Giant Leap for Womankind

This news makes me realize that a change is underfoot, and it’s in the lens through which American businesses view pregnant women. Marissa Mayer’s track record in business is proven. The idea that “baby brain” might hold her back– or that she wouldn’t be able to represent her own interests and commitments long-term at the negotiating table honestly– are gone. It is a historic moment to witness the transparency– that Mayer is facing both becoming CEO and becoming a mother head-on-and to see that Mayer believes she can both turn a failing company around and raise a healthy son.

Learning that a huge corporation does not see pregnancy as an issue to overcome is a sign towards Mayer’s peers who might be wondering how they, too, might be able to have children. Finding out that the Yahoo! board did not express hesitation in a pregnant CEO (and that they’re accommodating her needs by moving a scheduled September board meeting from New York City to Sunnyvale) is a giant leap for womankind. If Marissa Mayer can take on a risky CEO-ship while six months pregnant with her first child, then it’s clear that not only is the path for women becoming less rocky, but it’s also becoming more accommodating of women who can decide their work-life balance on their own.