Simpson, 23, recently engaged to rocker Pete Wentz from the band Fall Out Boy, danced around Ellen's question of whether she was expecting, People.com reported Thursday.
"Well, that has been going on for quite a while. That is something that I choose personally not to discuss," she responded.
She cleverly jumped to another conversation topic, the report said.
"Do I look like I had 10 cheeseburgers or something? Because I don't think I do," she said.
The slender star did promise DeGeneres not to keep her possible pregnancy a secret as long as singer/actress Jeniffer Lopez did last year.
"I swear. I promise you that. I give you my pinky on that," Simpson said before locking pinkies with DeGeneres.