Chan can be seen in a photograph already displaying a baby bump. In fact, the Zuckerbergs decided to finally announce it because the pregnancy is now far enough along that the risk of losing the baby is very low.
The 30-year-old had suffered three miscarriages during their three-year marriage.
Zuckerberg wrote on his Facebook page that his wife's miscarriages were "a lonely experience." They wouldn't talk about it with their friends.
He now says this is a great opportunity to begin a dialog.
"In today's open and connected world, discussing these issues doesn't distance us. It brings us together. It creates understanding and tolerance and it gives us hope," he said in the post.
"What most people don't realize is how common miscarriage is," Pacific Fertility Center's Dr. Carolyn Givens said.
Medical reports show that 10 to 25 percent of all clinically recognized pregnancies will end up in miscarriage.
"Most of the time it's because the embryo itself doesn't have everything it takes chromosomally or otherwise to make it to live birth, so this is nature's way of taking care of it," Givens said.
As women get older, the risk of a miscarriage increases.
"Somebody of his profile, too, bringing it up and saying hey it's OK and everyone goes through it and I think it's just as hard for a father as it is for a mom to have this experience of loss," mother Corynne Cooper said.
"I think when you share your stories, it makes it just a lot easier to bond and to get through difficult processes and know other women are going through the same things," mother Melissa Hamilton said.
The Zuckerbergs are expecting a baby girl.