My friend gave birth to a beautiful baby girl yesterday. Her experience reminded me once again of the first rule of natural childbirth: you have to decide it. Unless the baby comes too fast, you have to decide ahead of time to refuse the painkilling drugs.
I have given birth twice without pain meds. And that was only because I decided to.
If you go into the hospital thinking, "I'd like to have a natural childbirth, but I'll just see how it goes," you are going to end up with an epidural or other pain meds.
Childbirth hurts! It is scary! You will get tired! And the kindly nurses will ask you if you'd like anything for the pain, even if you write on your birth plan that you don't want them to ask you that.
If you want the pain medication, that is your choice. But if you truly want a natural birth, you must decide to give birth without pain medicine.