The couple revealed the news in a video posted on Uninterrupted,the online platform created by LeBron James.
"We know we're not the only family going through this, who has been through this or who will ever go through it," Smith's wife, Jewel Harris, said in the video. "That's why we decided to share what we've been going through with you guys. Please keep us in your prayers, and we'll do the same for everybody else."
Smith has not played since December after undergoing surgery on a fractured right thumb and is expected to be out a total of three months. In the video,Smith thanked fans for checking in about his injury and said it "is what it is."
The Cavaliers guard had announced Harris' pregnancy in October in a video also posted on Uninterrupted, when he confirmed his contract extension with the team.