I have seen babies riding very low and pressing on that cervix for weeks, but not start labor until baby was good and ready.
I've seen babies ride very high until late labor, barely touching that cervix and sure enough labor started on its own and proceeded to the finish just fine when baby was good and ready.
I have heard this myth about breech babies not starting up labor because butt is not 'hard' enough to stimulate cervix---in fact, I heard it first from an OB but I do not believe it....I think it IS a myth.
I've also heard midwives speculate about this or that seemingly dysfunctional labor and how they worked to get baby down and well applied to cervix (in head down position) to make labor move faster...but again, I've seen moms dilate and otherwise proceed just fine without head well applied so I think this is a myth, too!
yes, it is a combination of signals from mom and baby both--biochemical signals--that are responsible for labor's onset. I even know a triplets mom whose 'presenting' baby (the one on the bottom) was transverse--no pressure of any butt or head on cervix--and she spontaneously labored to 7cms before u/s showed the transverse lie and she was sectioned...I've no doubt she woulda gone to fully dilated before long (it only took her 5hrs to get to 7), but the OB would have none of it.
So forget that concern, and go ask your midwife to show you the research that supports this--maybe you will help her learn something new, and get her to STOP helping breech mamas believe their babies and bodies don't know what they're doing! But at least clear your own head of this and all other breech birth garbage, cuz you need to be trusting and strong and all positive right now!