My shih-tzu is about 10 years old. Recently I was dog sitting my son's beagle. My dog mated once with another shih-tzu. She got pregnant and ennded up needing a c-section. She had 2 puppies who both had breathing problems and she would not care for them. We did our best but both ended up dying. While I had my son's dog hear they mated. She didn't seem to be in heat so I thought they were safe together. Is there any way she could be pregnant at this stage in her life and would she be able to safely carry and deliver beagle pups?

It they did she is, you should take your dog to the vet, this is like letting your grand mother have children, you need to spay or neuter some one,

Please refer to this site, Pet Education it will be helpful in answering questions for you. You have repeated the same mistake twice, you either can not watch your sons dog, or some one needs to be snipped

National Stats
The sad fact is once a puppy is past its cuteness; or a dog displays behaviors we don't know how to deal with, many canines are discarded like old newspapers. On average 100,000 dogs and puppies are listed on www.petfinder.com, daily. It is reported by the National Council on Pet Population Study and Policy, from the 5000 or so US agencies who responded to the survey, that over 2 million dogs enter shelters annually. Of those 27% are relinquished by owners, 42% are turned in by animal control, 31 by other sources, of these dogs, 56% are euthanized.

Control the pet population Spay or Neuter

What makes you think that they actually mated? Did you actually see them tied together? I'm sure since she's 10 years you know when she's in heat or expected to come into heat. A female will not let a male mount her until she is ready. If she's had complications before with pregnancy then I would be concerned with the pregnancy and whelping. Then is also an option of aborting puppies, with out spay, but if I can remember correctly I think it's very limited in the US. The other option is if you definitely believe that she may be pregnant then you should run some blood work, and if she's healthy and has no other history which might concern a doctor for a dog to be under anethesia spay her which will in turn abort the puppies of course. There are lots of dogs that give birth when they are geriatric with no problem and others that cause premature fatality. It's in the best interest that since she is old and had other complications to talk to a vet about the possibility of her being pregnant and see what his advice is.

Your vet is you "other family doctor" he's there to help you and your pet never be afraid to call and ask for help.