Video courtesy of "Pregnancy Videos" https://www.facebook.com/PregnancyVideo?fref=photo
The mom's position is one of the most important things for a good birth, On-the-back position closes the pelvic outlet and makes the passage much harder. Many babies get "stuck" because gravity is not helping and because the outlet is smaller when mom is on her back. Any position that causes the sacrum and coccyx to be stuck and unable to "flare out" severely restricts and constricts the shape and the size of the outlet. Mom on back positions are the worst. In this video you can also see how important it is to have proper alignment of the pelvis so that bones, ligaments and muscles are balanced, symmetrical and pulling evenly.
As chiropractors whose emphasis is on pregnancy work, one of our main goals is to create balance in the mom's pelvis and spine, as well as to teach her techniques to maintain these corrections.