http://www.yorkietalk.com/forums/bre...t-breeder.html
The library has some excellent articles about considerations prior to breeding
I have posted a link above.
The mother controls the size of the pups. So given the mom's weight is not from obesity, then unless she comes from a long line of smaller Yorkies, this potential breeder should not count on small adults.
Pelvic structure is very important in free whelping. A vet should be able to tell if this female has a "good" chance of free whelping. And I would find a reproduction vet to go to.
There are also many threads on here, where I and others have elaborated on the pre breeding tests. And unless you have them done at show clinics where the cost is pretty reasonable the price can easily add up to over $500. Also the male has to be tested for the same things as the female.
I think many folks just think after all dogs are just animals and animals in the wild give birth all the time. Well true, but consider dogs have been domesticated for thousands of years, and where natural selection does still operate in the wild; not so when humans make the decisions regarding breeding. Also true there is a very high incident rate of puppy and dam mortality in the wild. Puppies born with less than ideal structure or with genetic defaults usually will not in the wild survive long enough to mate.
Quite frankly; there is no short or inexpensive way to breed healthy and good representatives of the breed.
For me I just can't see why one would put their female at risk, and the resultant costs both financial and emotional that comes with raising a litter of puppies.