In a blog post, the 40-year-old said she planned to approach the pregnancy and December delivery as she did with her first child three years ago, by "taking limited time away and working throughout."
"I've shared the news and my plans with Yahoo's Board of Directors and my executive team, and they are incredibly supportive and happy for me," she wrote.
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Following the birth of her son Macallister in 2012, Mayer famously took just two weeks of maternity leave and worked right through it.
Her decision to return to work so quickly elicited a mixed reaction — praise for showing that a new mother could continue to steer a major multinational corporation, and criticism for failing to set a realistic expectations for working moms in the U.S.
Carrying identical twin girls came as a surprise, Mayer wrote in her blog post, noting that she had no family history of twins or any other predisposing factors.
"Zack and I have embraced the surprise and are very excited about these new additions to our family," she said of her husband, lawyer and investor Zach Bogue.
To read the full blog post, click here.