hi janw, my bitch also had a discharge like this very early on in pregnancy, and i at first thought it was an infection but the vets told me it was nothing to worry about. I know they sometimes get a discharge later on, but my bitch only had this greeny mucous discharge from about 5 days in for about a week, and that was the only discharge she had throughout the whole of the pregnancy.
But i would probably have the vet check her out as i did, just in case, x