Yorkies ...like so many of the other small breeds
Have trouble carrying/whelping their puppies a lot of the times
That's part of the reason that they are so expensive.
Any time you breed your dog , you have to understand the RISKS
For every good ending you read about....
You can find that many with sad results.
I also have an under 3 lb male
BUT he came from a 7 pound female and 6 lb male.
So chances are if I ever bred him to a tiny 3-4 pound female she would be in trouble.
Any time you breed any female you have to be prepared for the worst.
Maybe even losing your mama.
I hope this helps
