foetus position

[Paragonidae]

in order for a foetus to come out right it needs to be in a certain possition (front legs and head streached and toward the birth canal). the question is how do the foetus "know" the correct possition. is it something like "chemotaksis" to the air as the cervix is open and there is exposure to air? I think this isn't the answer because I thing the foetus is already on the correct possition before the amnion is broken...
I am not sure this is the right forum for this question so please direct me to the correct place. thanks.

[Darby]

My understanding is that the fetus is shifted, rather than shifting itself, over the last trimester, but I don't know the mechanism.

[Paragonidae]

either way the question still remains what sensors know which way is which and where is the head of the foetus. also conceder foetal dystocia