The same as any other dog- gestation in chihuahuas takes between 60 and 64 days. This is a special concern for tiny breeds, to aviod large puppies and c-section.
Sixty three days is the average gestation period for most dogs. However, chihuahuas can be as low as 56. Generally between 56-67 is a good estimate. The dog's overall health can effect the gestation period.
Dogs in general have pregnancy term of about 62 days. Chihuahua typically give birth a couple of days earlier, but it varies widely. Often larger litters lead to reduced pregnancy terms.
The gestation period in ALL DOGS, no matter how big or how small, is nine weeks. Roughly a little more than two months. Keep an eye on your dog when she gets close in case she needs a C-section.