8 hour labour with breech DS was no problem (until c-section). On my hands and knees over the swiss ball (or standing) in the shower. Posterior, quick labour with DD and SPD was drug free and fine. I only insisted that there was no pushing my legs back beyond hip level and you stay within the realm of your comfort. There are other birthing positions available to you which are better anyway than on your back (unless that suits you!!)