How small is too small for pregnancy?

I know someone who had purchased a sibling of my daughter's little 3 pound chihuahua, Buffy. Her dogs weighs more than Buffy (probably 3 1/2 pounds) and is -- what I consider - teacup size. She may be pregnant from a male chihuahua weighing probably 4 1/2 pounds. It was an accidental pregnancy and she'll be taking her to the vet next week.

Buffy's mother is not teacup size and gave birth to 7. I'm hoping this dog will be ok.

Question: Can a teacup chihuahua safely give birth to puppies? If so, do you know how many puppies they would usually have?

I would ask the vet - I am sure some teacup chihuahuas do just fine, but with a dog that small, I am sure the vet will want to monitor her closely! Let us know what he/she says.

I know with Boston Terriers, the litters are always very small (1 or 2) and 99% of the time they have to do C-sections. I'm not sure if it's because they are small dogs or if it's because Boston Terrier heads are rather large! :D