For women who are told "not to push" even when they feel the urge:
The Anterior Cervical Lip: How to Ruin a Perfectly Good Birth
This article is a must read. I can tell you that I have pushed two babies out without being fully dilated. I feel the urge to push and can feel the baby's head pushing my cervix open as I push. That's actually the part of birth that I find to be the most painful. It's quick quick going after that though and baby is soon born.