I started sitting on a birthing ball at 30 weeks with my first baby to relieve back pain and started bouncing gently at 33 weeks. I got a little more vigorous with my bouncing each day, and my baby was down in place at 36 weeks. Then, since I was at the "safe point" to give birth soon and baby's lungs were fully developed (monitored through ultrasound with the best tech around), I started bouncing my butt off at 36 weeks! I also started taking a warm bath nightly and put lots of EPO in the water, took EPO every night by mouth until 37 weeks when I started inserting it as well. I also started raspberry leaf tea to help build stronger pushes at 30 weeks. Anyway, I gave birth at 38w5d, but I pulled out all the stops.
My sister only used the birthing ball starting at 35 weeks and she gave birth at 38w5d too.