The fact that porcupines have quills when they are born has led to the supposition that they either take birth with no quills or must always be born headfirst to prevent injury to the mother.
So, are porcupines born with quills? Yes, porcupines are borns with very soft quills and young at birth are surrounded by a tough membrane that protects mother porcupine from injury. The quills of newborn porcupine harden after a couple of hours.
There is likewise a birth membrane around the young of most other mammals. So, the position at birth really makes no difference.