Pregnancy scare

His wife was in labor with their first child. Things were going pretty well when suddenly, she began to shout, "Shouldn't! Wouldn't!
Couldn't! CAN'T!"
Panicked, the husband phoned their doctor and told him what was happening. "Doctor, this is Mr. Smith, and my wife is acting very strangely! She just started calling out 'Shouldn't! Wouldn't! Couldn't! CAN'T!', over and over again, with an occasional Isn't and
Won't! thrown in. What's going on!? Should I be worried? What should I do? Just what is wrong with my wife!" he cried.
"Not to worry." said the doctor. "Get her to the hospital, I'll meet you there."
"But what is it!!?" queried the husband.
"Nothing out of the ordinary," assured the doctor. "It's perfectly and just part of her pregnancy. She's just having contractions, that's all!"