Mayer said she is due in December and it appears she won't be taking full advantage of Yahoo's parental leave policy.
"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.
Mayer was back to work soon after she gave birth to her son in 2012, the same year she took over as Yahoo's CEO.
"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 said. "I want to thank them for all of their encouragement as well as their offers of help and continued support."
The announcement of her pregnancy comes as Yahoo prepares to spin off its stake in Chinese e-commerce site Alibaba into a new entity called Aabaco Holdings. The move is expected to close in the fourth quarter of this year.
While Mayer's quick maternity leave drew some criticism that she was setting an unrealistic example for many women, she later followed up by extending Yahoo's parental leave, offering mothers up to 16 weeks of paid maternity leave, which also applies to adoption, foster child placement and surrogacy, and eight paid weeks for fathers.