Ferguson, 48, took to Twitter on Wednesday to announce the big news. "Holy crackers! Mrs F is pregnant. How did that happen? ... Oh yeah, I know how. Another Ferguson arrives in 2011. The world trembles."
The late-night host, who married Wallace in December 2008, has a 9-year-old son from a previous marriage.
Reps for Ferguson did not immediately respond to TVGuide.com's request for comment.