And now just who would they tell? The question is, are dogs able to sense that your body chemistry has changed, and to attribute this to pregnancy. As to the former, I assume the canine of the house to be quite familiar with the odor of the mistress of the house, and likely keenly aware of changes in cycle. But the question still remains if they care about menstrual changes. I assume they can sense (smell, etc) many of the changes, but do they care??
I one time had a dog that knew what I was talking about. I could place several different things in the floor and tell her which one to bring me and she would. What was so crazy about it she wasn't trained she knew the words.