hi again laura!! when I gave birth my weight had shot up to 15 stone, the consultant and aneathatist seemed to think that because of my weight Id need an epidural?!?! why?? any way I gave birth naturally with just gas and air, it was a long labour but only 12 hrs in established labour (4 days of slow!!) so I guess its not just weight but your overall fitness level!!
I do know that the more worried and scared you are the more difficlt your labour will be, I was relaxed throughout and really didn't find it too bad the pain was manageable etc etc, ask your mw if there are any traumatic birth classes you can go to and try to get on top of your fears so you can make this pregnancy and birth a positive experience for you!!