My dog Vanilla was pregnant when she was spayed. We had no clue, because she was so thin. She was pregnant with six puppies, and then you wouldn't have believe how thin she was after she was spayed. It was pitiful. She was basically almost starved, but because she was pregnant she didn't look quite as bad. She weighs 25 pounds now, right after her spay she weighed 11 pounds.

Good luck to your doggie, I'm sure all will go fine. Vanilla was fine, even though she was fairly late term as well.