Zuckerberg, Chan share on Facebook: It's a girl!

"This will be a new chapter in our lives," Zuckerberg wrote in a Facebook post. "We've already been so fortunate for the opportunity to touch people's lives around the world . . . Now we'll focus on making the world a better place for our child and the next generation."

He added that during their years-long effort to start a family, Chan had three miscarriages.

"You feel so hopeful when you learn you're going to have a child," Zuckerberg wrote. "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. Most people don't discuss miscarriages because you worry your problems will distance you or reflect upon you — as if you're defective or did something to cause this. So you struggle on your own."

Between 10 and 25 percent of pregnancies end in miscarriages, according to the American Pregnancy Association. It is a surprisingly common occurrence, but women and their families often cope with the loss alone. "Women are often left with unanswered questions regarding their physical recovery, their emotional recovery and trying to conceive again," the group said. "It is very important that women try to keep the lines of communication open with family, friends and health care providers during this time."

Chan, 30, and Zuckerberg, 31, met in 2003, while both attended Harvard. He never graduated, focusing instead on launching Facebook. Chan, a former teacher, is a pediatric physician at the University of California at San Francisco. The couple married in 2012.

Zuckerberg said on Facebook that he and Chan decided to share their story to help others who have the same experience.

"When we started talking to our friends, we realized how frequently this happened," he wrote. "We hope that sharing our experience will give more people the same hope we felt."

Chan and the child are healthy, Zuckerberg added.