This video of Magali Dieux provides a wonderful example of the power of vocalization during labor. She uses a range of tones, low oms that sound like Buddhist chanting, ahhhs, descending scales, some louder, some breath-soft (pardon the multi-lingual voiceover that sometimes obscures her sounds). Here is a link to the original video.

Naitre_enchantee
Uploaded by magalidieux