Short of having a severe pelvic deformity of some kind, the only way to tell if a woman is able to birth a baby is for her to labor. If the baby won't come out despite everybody's best efforts to help that happen--and I emphasize best efforts--then a cesarean may be necessary. A doctor who is discouraging vaginal birth for less than compelling reasons during pregnancy raises a huge red flag. I recommend you find out your ob's cesarean rate ASAP. If it is much over 15%, the maximum supported by numerous studies and the World Health Organization, or if your ob doesn't know or won't tell you ("I only do them when it's necessary"), take that as a clear sign to find someone else. Even if you decline a recommendation to plan cesarean surgery, you will be laboring under the care of a doctor who has already indicated a preference for cesarean, which means you cannot trust your doctor's judgment.
-- Henci