
I have known pregnant dogs continue to be shown (conformation) but for me, regardless of any stress/travelling etc.etc. I'd be more concerned about the risk of picking up some infection doing the rounds, than anything else. When we did our litters, we curtailed any showing or going where there were multiple dogs around. And that meant all our hounds, not just pregnant mum.
For me, the well being of my hounds always comes first.
ps I know, first hand, of somebody with a pregnant bitch who took another of her hounds to a social occasion.... and brought Kennel Cough back to the house. She lost a number of the newly born puppies after mum had picked this up.