My sister phrases it more professionally, I assure you, when interacting with patients. She encourages them to put all the energy they're putting into screaming into pushing. Making some grunts, groans and noises of exertion are, of course, normal during labor. Even the 'moo'-ing thing some women chose do to can be beneficial. But some women scream like maniacs, like they're auditioning to be a scream queen for Wes Craven. They get more focused on reacting to the pain than pushing, so she (and other nurses & doctors) try to get them to put all the energy & vocalizing (which can exhaust you) into a more productive task. Child birth is terrifying, especially for first time moms & my sister has excellent bedside manner. She's even trained herself not to roll her eyes when women get 'push gifts'.
She's made the constipation comparison to me because (as I'm sure many know) the pushing motion for giving birth and having a bowel movement are very similar. We don't scream when you bear down to take a shit.