I think you are right Buttonbear, its the fear of the unknown - how much it will hurt, how long it will last, will it go ok etc.
Also my other half is the most supportive loving partner, however he is terrible with hospitals and has told me he loves me and the baby and will be there for us both until the day he dies but he just can't be in the room while I actually give birth. I'm hoping he will change his mind (my mum thinks he will) but at the moment my plan is for him to wait in the labour waiting room and mum to be in with me when the time comes. Half of me feels upset as I really want him there holding my hand, the other half of me totally understands. He had a small op last year on his foot and he was a nightmare, not with the pain or anything like that, just while we were waiting to go in he was saying its so hot in here and getting really flustered, which is odd as he is the most chilled out person I know with absolutely everything else in live except for hospitals! xx