"Cilla and our child are both healthy, I'm extremely excited to meet her and our dog Beast has no idea what's coming," he wrote. "In our ultrasound, she even gave me a thumbs up 'like' with her hand, so I'm already convinced she takes after me."
Zuckerberg said the couple, who have been married for three years, were expecting a girl, but didn't give an expected due date.
Zuckerberg first met his wife while they were both at Harvard. He would eventually drop out to run Facebook, while she remained to finish out her degree before going onto medical school at the University of California, San Francisco.
But the announcement did not come without its own heartbreak, with Zuckerberg acknowledging that the couple has been through three miscarriages in the past.
"You feel so hopeful when you learn you're going to have a child," Zuckerberg said. "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."
He said that as our society grows more connected people should no longer feel the need to suffer alone and use those experiences to grow closer. He said both he and his wife hope that by sharing their experience, it "will give more people the same hope we felt and will help more people feel comfortable sharing their stories as well."