Batman Arkham City Easter Egg - Joker Junior?!

*Possible Spoiler Alert*




•Go to the Steelmill (Joker's First Hideout)
•Go to the Joker's Office (Manager's Office)
•Here you will see Harley Quinn's costume from Arkham Asylum,which is already interesting, but there is more!
•Look at the floor next to the outfit, you will see a pregnancy-test, A positive pregnancy-test to be precise.

What could it mean: Just a joke or a serious plotline for the next Batman game?

P.S. In the credits, if you listen long enough, you can hear Harley sing a lullaby: "Hush, Little baby. Don't say a word. Momma's gonna kill for you the whole damn world."