A meta-analysis of selected studies on hypnosis for childbirth found that women who used hypnosis were:
51% less likely to use drugs for pain relief (38% of the hypnosis group used pain meds, compared to 74% in the control group)
70% less likely to have their labors augmented (11% in the hypnosis group were augmented, compared to 70% in the control group)
67% more likely to have a spontaneous vaginal delivery (no induction or c/s)
Despite it being a meta-analysis, the sample sizes are still kind of small, and I imagine that any type of childbirth preparation would result in a reduction in interventions compared to the norm, but these stats are still pretty impressive sounding.