Hannigan's pregnancy also seemed perfectly timed with her CBS sitcom, "How I Met Your Mother." Her character was also pregnant this season, saving producers from worrying about how to hide her baby bump.
The actress poked fun at her growing stomach in in early May after Jessica Simpson finally gave birth to her baby girl.
"Congrats to Jessica Simpson! Does this mean I now have the biggest baby bump in Hollywood?" Hannigan tweeted.
Hannigan and Denisof married in 2003, after working together on "Buffy the Vampire Slayer." Denisof has also appeared a recurring character on Hannigan's CBS sitcom, "How I Met Your Mother" and can currently be seen in "The Avengers."