I attended a lecture the other night by a DO regarding osteopathic
manipulation and labor mechanics.  The DO talked about how the pelvis is a
container and the uterus is a container within a container.  She said she is
able to influence the lie of the baby by making sure that the pelvis "floats"
and is balanced during pregnancy.  She said that in a multiple pregnancy that
the pubic symphysis (spelling???) can spread up to 4 inches!!!  The hormonal
softening of the cartilege and ligaments is designed to accomplish the
"floating" of the pelvis.  If there is a pelvic torsion, one part of the
pelvis will not be aligned properly and can cause a distortion of the pelvic
outlets. Babies lie so that they are comfortable.  From the description she
gave, it sounds like when there is a persistent posterior position, the
pelvis shape guides the baby into that type of lie (for comfort reasons).
 The actual birth is another event that can distort the pelvis, especially if
the tailbone is broken in the process.  When the softening goes away after
the birth, if the pelvis is not balanced, it will retain the last shape taken
and can affect the next birth experience.

I feel like I now understand why my own labor failed to progress, why my son
was a persistent posterior and why the ultimate C-section.  I had a pelvic
torsion, labored in a mechanically diadvantageous position, etc.

It is too bad that the science of mechanics is not included in obstetrics!

learning more sensible info the longer I live.
Martha Brower RD LD IBCLC