My sister had twins, now 1 1/2 yrs old. She had many concerns like you :O) My response is to let you know that she carried to 38 weeks and delivered both boys vaginally without any complications. Call her lucky, or whatever, but I just wanted you to know that there are stories out there with a successful happy ending :O)
One thing that I believe helped her alot, was instead of planning on all of her help AFTER the delivery (with frineds and family) she called them in weeks BEFORE she delivered. She already had a then 2yr old daughter, and wanted help with her, so she could lay down and rest her body as much as possible to avoid early labor. She also went as far as to hire a Nanny to help her keep up with the everyday needs that a mother holds. I know this isn't possible for everyone, but I truly believe that this helped her carry as long as she did, and also helped result in a successful delivery. She was always relaxed and rested, and so were her babies :o) So, if possible, ask your friends and family to help you with errands, etc.... so you can make sure you're resting your body. If possible, maybe hire a housekeeper to help relax your mind that your house is being maintained even while you rest :o)
Try not to worry too much, just share your concerns with your Dr, so they are prepared for your delivery to accomodate your pain when it is time to deliver :o)
I'm sure everything will be just fine. Try to enjoy your little miracles that are growing inside without too much worry :o)
Again, Congratulations to you and your family. What a blessing!