A Teacup Chihuahua is not a breed or version of the main breed. It is a term used by bad breeders or scammers to describe a non-standard sized Chihuahua. The Teacup is not officially recognized by any Kennel Club as an independent breed. It is a catch-all phrase used to describe any "mini" Chihuahua that is smaller than average or sometimes a chihuahua in general as a selling point. While Chihuahuas themselves do exist and they are the smallest of all the dog breeds, there really is no such thing as a Teacup Chihuahua.  AKC Standard is 3-6 pounds.

If you do find a legitimate breeder that has a puppy under 3 pounds, be prepared for possible long term health issues.  Such as Hypoglycemia, Liver shunts, Kidney issues, etc.

Genetic testing of the parents is extremely important to help eliminate the possibility of health issues but certainly there are nothing is 100% guaranteed.  

Most veterinarians are not specialized in the care and treatment of tiny dogs.  I have been to several ER vet clinics that have almost killed tinies with hypoglycemia because they didn't get them eating in addition to giving them glucose drips.

PLEASE DO YOUR RESEARCH.  EDUCATE YOURSELVES. 

How to Prevent Low Blood Sugar in Puppies

Providing proper nutrition on a routine schedule is crucial. Small breed puppies should be fed three to four times a day. Ensure you’re feeding a commercial puppy diet that is formulated for growth.

As other ailments can predispose to hypoglycemia, any signs of illness must be attended to. So, if your puppy is coughing, has diarrhea, is vomiting, has appetite loss, or seems lethargic, waste no time in seeing the vet.

Lastly, make sure to keep your puppy nice and warm at home.

Treatment for Hypoglycemia in Puppies

If your puppy is conscious but showing signs of hypoglycemia (see above), start by offering tasty food that he or she will want to eat, such as canned food. If your puppy will not eat, a fingertip of Nutrical may make all the difference. This product is frequently provided by both veterinarians and breeders for use in toy breed puppies. It consists basically of a malt-flavored paste with sugar and vitamins. Some puppies will readily lap it off fingers and others will only take it if it’s smeared on the roof of the mouth. In most cases, the puppy will respond very quickly to treatment, within 5-10 minutes.

If your puppy is listless, comatose, or seizing, a small amount of Karo syrup can be rubbed on the gums for first aid. It will absorb through the gums; actual swallowing is not necessary. Beyond this, the puppy should be rushed to an animal hospital for treatment.

With any signs of hypoglycemia, make sure your pup is warm by wrapping them in a blanket. When the blood sugar drops, puppies can’t regulate their body temperature. It’s important to keep the dog warm until the glucose level rises.

The key is prevention by ensuring that the pet is consuming frequent meals