If your dog was never vaccinated for parvo than there would be a chance of parvo. Please tell me she has been vaccinated for parvo and you did not breed an unvaccinated dog!
Pregnancy is very stressful on a body of any species and the stress can bring out dormant parasites, or increase susceptibility to other disease such as pancreatitis or colitis.
Please have her evaluated by a vet!
I am so sorry to hear this. I hope your dog is alright in the end. I think that if you have hope everything will turn out fine, but I would consult a vet as soon as possible, and watch her carefully, don't let her out of your site, because you never know what could happen. Hope everything turns out well...
I am definitely not a vet but I do know that blood in stool is a very dangerous symptom of a potentially deadly problem, especially if she has pups. you should take her to a vet IMMEDIATELY. I hope everything goes alright but be prepared to hand raise the puppies.