"I'm so excited to share this news with you!!!" the professional dancer and television personality tweeted. "Thank you for all of your support!"
"It wasn't planned, but when it happened, I thought, 'This is perfect -- I'm ready to be a mom,'" Trebunskaya told US Weekly. "This is something really good for me and fulfilling, and it'll give me a whole new meaning in life. I'm really looking forward to it."
Trebunskaya called the baby's father "very supportive," but said she preferred not to share his name.
"Good Morning America" revealed the celebrity dancing competition's 17th season cast on Wednesday morning -- it will include Amber Riley, Bill Nye, Leah Remini and Jack Osbourne, among others.
"I love being the show, and I'll miss it a lot, but I'll still be around visiting," Trebunskaya -- who was notably absent from the list -- said of skipping a season. "I'll be their biggest cheerleader."