The chief executive of Yahoo, Marissa Mayer, has announced she is expecting twin girls in December, but plans to take "limited" time off.

In a blogpost, she said that because this was "a unique time in Yahoo's transformation", she planned to take a similar approach to when she had her first child and "work throughout".

Ms Mayer famously returned to work two weeks after giving birth to her son.

In its corporate blog, Yahoo said it was "extremely happy" for Ms Mayer.

Forty-year-old Ms Mayer has been chief executive for three years at Yahoo. She is in the process of changing the internet firm's focus away from the traditional desktop and towards mobile and video adverts, in order to increase sales.

In the company's last earnings report, she said she was encouraged by an increase in revenue from that division, despite recording a net loss of $21.6m in the quarter to 30 June.

Yahoo is also in the midst of spinning off its stake in China's Alibaba.

Ms Mayer said she was surprised by the news that she was expecting twins, since there is no history of it in her family, but that she and her husband, start-up investor Zachary Bogue, had "embraced" it and they were "very excited".

"Moving forward, there will be a lot to do for both my family and for Yahoo; both will require hard work and thoughtful prioritisation," she wrote in her post.

"However, I'm extremely energised by and dedicated to both my family and Yahoo and will do all that is necessary and more to help both thrive."