The IV is for more then just fluids, although staying hydrated is important. You can't drink anything while in labor (only ice chips). It is all a precaution just in case you need an emergency C-section. Anything can happen even with the best planned situation. If something goes wrong (I hope nothing does!) you would want them to be able to get you in the operation room and get your baby out as fast as possible right? Of course, and having an IV will allow them to do that. If you refuse the IV (which I'm not even sure you can) you will only be putting yourself and your baby in possible danger.
So please, in the best interest of you and your baby let the doctors do what needs to be done to ensure that you have a healthy baby.
Good luck and congrats to you!
-Brit