This is a fascinating read by Jean Sutton.  Here is the link to the full article, below are some passages I found partially interesting….

"To understand real, physiological second stage labour, we must learn about the ‘rhombus of
Michaelis’. This is the kite-shaped area of the lower spine that includes the sacrum and three lower lumbar vertebrae. We may learn that it has limited flexibility during pregnancy, but nothing about its role in labour.  As second stage labour begins, the rhombus of Michaelis moves (this is ‘the
opening of the back’ which the Jamaican midwives spoke to Sheila Kitzinger about). Midwives working with mothers who give birth on all-fours or kneeling without wearing clothes will have seen this as a large ‘lump’ that suddenly appears on the mother’s back. It has been suggested that it is the baby’s head pushing the sacral prominence outward, but this is not so. It is the rhombus of Michaelis moving back – up to 2cm. At the same time (but not visible to the observer) the wings of the ilia fan outwards, thus increasing the internal dimensions."

"Someone decided that a rounded back would be protective – without realising that bringing the
knees up brought the spine and the symphisis pubis so close that, unless the baby’s shoulders were already in the transverse, they would be stuck at the brim. Then came the ridiculously long second stage labours. If a baby is lined up properly, and his mother keeps her knees down, half an hour is normally plenty for a first baby and ten minutes for a subsequent one."

"Any position that brings the knees towards the abdomen reduces the space in which the baby can move. It will also increase the chance of the baby being pushed into the back of the pelvis and into the back of the pelvic floor, instead of pressing against the symphisis. From here a major pushing effort is needed to get the baby out, and the likelihood of tearing the perineum or needing an
episiotomy rises."

"The use of epidural anaesthesia during labour, even the walking kind, must have had an effect on the normal movement of the rhombus of Michaelis. If the birth nerves are not stimulated, how can the reflex occur?"

Not a surprise that the artificial knees-by-the-ears position that most hospitals employ during pushing is counterproductive.  And, again, we see how epidurals interfere with the normal course of labor and delivery.  The more I read about the subtle hormonal chances that occur within a woman’s body during labor and delivery, the more I realize that there is so much that is ignored during your typical hospital birth.