Showing Broodmares

Breeding and showing are 2 things I have not done a lot of, but as I continue to be involved in Morgans I hope to do more of both.  I’m curious what experience folks have had with showing a mare while she’s in foal.  I’m sure results vary from horse to horse depending on their past show experience and temperament.  But in general how are bred mares able to handle the stress (both mental and physical) of maintaining a show schedule?  And how long into their pregnancy are they typically able to keep it up?