
The risky point in a canine pregnancy is the second trimester after the eggs implant in the uterus and placenta is established and before most foetal development takes place (so 3 to 6 weeks).
This is the stage when absorption takes place, and abnormalities in development occur and the foetal units are influenced by what the bitch encounters (re poisons infections etc).
so no I would not take a bitch in her second trimester to any show, large scale doggy event etc.
The first trimester the units are free floating and not linked into the bitches circulation, so safer, but of course for the first half of that period the bitch will still be in season, and after 6 weeks she will be shwoign her pregnancy too much to show.