
Hi,
I brought my book of the bitch home and it basically says that you have two options: 1) let the pregnancy continue 2) have the bitch spayed which will involve the removal of the uterus and foetuses. However, I know there is an injection.
According to 'The complete book of dog breeding' (Dan Rice DVM) There are three options when a termination is being considered. 1) Estrogen administraion - Estradiol, Dan Rice is of the opinion that the risks involved do not support its use. 2) Prostaglandin - removal of progesterone source which basically causes the bitch to abort or 3) spaying.
But, this is all from books, I am no vet and I seriously urge you to go and discuss this with your vet if you are concerned that a mating may have occured without your knowledge. Generally from my reading on this the sooner you go and discuss this with your vet the easier it is going to be for it to be resolved and the easier it is going to be on your bitch.
Good luck and again let us know how you get on xxx