I think Rhea Dempsey quotes research that says that (forgive me if I'm wrong, it was 2 years ago I heard her talk) only 3% of hosital births in Australia are completely without intervention. Apparently the WHO estimates that intervention is medically necessary in about 10% of births. Scarey stuff.

ETA: my only birth was not natural. Had gas, epidural and then forceps. I don't believe any were necessary, though the epi may have ultimately necessitated the forceps. Of course, I very much believed that I HAD to have the epi at the time... hoping to get past that this time!