Yahoo CEO Marissa Mayer announces she's pregnant with twins

Yahoo CEO Marissa Mayer said Monday that she is pregnant and expects to give birth to identical twin girls around December.

As with the birth of her son three years ago, Mayer plans to limit the amount of maternity leave she will take. The 40-year-old CEO wrote in a Tumblr post that she had already informed Yahoo's board of directors and executive team of her pregnancy.

"Since my pregnancy has been healthy and uncomplicated and since this is a unique time in Yahoo's transformation, I plan to approach the pregnancy and delivery as I did with my son three years ago, taking limited time away and working throughout," she wrote.

"Moving forward, there will be a lot to do for both my family and for Yahoo," Mayer wrote. "Both will require hard work and thoughtful prioritization."

The announcement comes as the struggling web company prepares to spinoff its 15 percent stake in Alibaba, the Chinese e-commerce giant that went public last year. The spin-off is expected to close in the fourth quarter of this year.

Mayer was tapped to be Yahoo's new chief executive on the same day she announced her pregnancy with her son in 2012. She was criticized by some for returning to work just two weeks after the birth of her son.

Mayer also stirred controversy a few months later by announcing the elimination of employee telecommuting -- arrangements often seen as indispensable by working parents and are often the norm at major tech companies. A few months later, Yahoo announced a more generous package of family leave benefits for employees, offering both mothers and fathers up to eight weeks of paid leave and giving mothers eight weeks of paid time off after pregnancy.

Mayer said she and her husband, Zachary Bogue, were surprised to learn she was having twins because she said there was no history of twins in her family. The announcement comes nearly three years after the birth of her son, Macallister Bogue.