Nobody with any sense, would look for, or BUY any "teacup" VERSION of any TOY breed. That is a "MARKETING PLOY" (called putting LIPSTICK on a PIG) that backyard breeders use, to sell sickly DEFORMED RUNTS, with HEALTH problems.
The smaller than normal RUNTS with have LIFE LONG, health problems that will COST YOU a fortune, and will have an MUCH shorter LIFESPAN than a normal-sized animal, of the same breed. They will also bring you nothing but HEARTACHE.
The term "teacup" is a RED FLAG to **RUN** from anyone advertising such animals for sale. They are not reputable breeders, and should be avoided - like they carry the PLAGUE!
Please GOOGLE "Health Problems in Teacup dogs" and do your own research, if you doubt any of us, or speak directly to your vet about this issue.