unexpected tie

Question
Hello Dr. Fry,

I have a 5lb. male rat terrier. Last evening my friend was over for a visit and brought her 3 lb. female chihuahua. It seems that the chihuahua was in heat. (It's the owners first dog and she was not aware that the dog was in heat.)
Well, the two dogs tied up. (I have had dogs all my life and explained to the owner to stay calm and not panic the dogs.)
We have 2 concerns. First, the chihuahua is only 11 months old. Also, though both dogs are small, the male was slightly larger than the female. Would there be health concerns should she have become impregnated? If memory serves me correctly, one tie does not necessarily mean the female will have pups and it may be 3 weeks or so before she shows symptoms.

Thank you for your time.
Susan

Answer
One tie is all it takes.  I would start planning for pups.  Ideally she should not have been bred that early but should be fine....make sure she is eating puppy food free choice.  Chihuahuas often have problems giving birth because the puppies heads are so big.  The other option is to have her spayed ASAP.

Pregnancy lasts 63 days plus or minus 5 days.  At day 25 or so fetal heartbeats can be detected with ultrasound and at day 42 skeletons can be seen on an x-ray to determine how many pups.