At this point, it might be funny to make an episode where someone finally notices this.
"Uh, how many months was it since you said you were pregnant, Luanne?"
"Six!"
"Uh...."
"No wait....twelve. It was twelve!"
"I see...."
Luanne finds out she was never pregnant to begin with, and then Lucky thinks his marriage is now false because he did it to make an honest woman out of her (Lucky logic), and so he leaves and Luanne gets upset and they have to find him.....see, there's a whole episode.