Zuckerberg, 31, and his physician wife Priscilla Chan, 30, announced they were expecting a baby girl in a Facebook post on Friday.

But their happy news did not come without much pain along the way.

The Facebook co-founder says he and his Harvard University sweetheart suffered three miscarriages over the past two years.

"We hope that sharing our experience will give more people the same hope we felt and will help more people feel comfortable sharing their stories as well." he said.

He said most people did not talk about miscarriage and struggled on their own.

"You feel so hopeful when you learn you're going to have a child. You start imagining who they'll become and dreaming of hopes for their future. You start making plans, and then they're gone. It's a lonely experience."

Zuckerberg said it was not until he and his wife started talking about it with friends that he realised many people had similar experiences before going on to have healthy children.

He said he and his dog Beast could not wait to meet the new addition to the family.

"In our ultrasound, she even gave me a thumbs up "like" with her hand, so I'm already convinced she takes after me."

"We're looking forward to welcoming her into the world and sharing more soon when she's ready to come out and meet everyone!"

Zuckerberg often takes to his Facebook page to make personal and corporate announcements and says his first child and wife "Cilla" were both doing well and "healthy".

The couple met at Harvard University and dated for more than a decade before getting married in 2012.