Ask the vet - Dog
I'm afraid my bitch might be pregnant. How do you go about terminating an unwanted pregnancy in dogs?
Vet at FirstVet answers:
If you witnessed your undesexed dog mating it is recommended to book an appointment with a vet to terminate the pregnancy (if pregnancy is unwanted). This is done by the vet who gives your dog an injection 2 days in a row. However, if your dog escaped when in heat and you do not know whether she mated it may be a good idea to wait a few weeks and then ultrasound her to see whether or not she is in pup. If she is in pup the injection is given just as described above.
The injection works well in most cases, but sometimes the foetuses are not resorbed (absorbed by the body) or aborted properly. This can be dangerous. An ultrasound is therefore recommended to ensure there are no foetuses remaining a week after the injections are given.