My dog Lucy is a small, just under 10 pounds. Little did we know, before her heat we didn't know she had started it that early then and had been with the neighbor's unneutered chow mix during a play date. This wasn't intended, and we are going to do our very best with the pups. No spay/neuter lectures please. She's going to be spayed as soon as she is through this. Now several weeks later, she's gaining weight, her abdomen is starting to swell, her nipples are slightly larger, she's sleeping more, and she's eating more. If she's pregnant, can I expect birthing problems because of the great size difference?