Well, I havent "researched" this but it is my initial THOUGHT that it would stall it, because....
Any other mammal, when in nature, will not go into labor or birth a baby until all stress is gone and they are in a comfortable atmosphere. If you have a dog for example, and they are birthing on their own and you rush in with 4 others admirine, talking loud, carrying on, etc and the dog is disturbed and uncomfortable, it will stop labor until the environment is "birth friendly" again.
Same as say a tiger in the wild. Not going to go into labor when there are stressors around.
Just a thought.
Edited to add. There is positive stress and negitive stress. Perhaps negitive stress would stall it, but positive stress could encourage it?