Thanks for the congrats on my fetus!" the 31-year-old wrote. "No secrets here; just thought it would be fun to see how big I could get before someone noticed."
Cody, whose real name is Brooke Busey, won the 2008 Academy Award for best original screenplay for "Juno." She is also the screenwriter behind the 2009 Megan Fox film "Jennifer's Body" and the creator of the Showtime series "United States of Tara."