Expecting a large baby is not a reason to plan cesarean surgery. Your odds of VBAC are better than 50:50 if you labor whereas if you plan a cesarean, they are 100%. Planned surgery for suspected large baby (macrosomia) has not been shown to improve outcomes, and you would be exposing yourself and any future babies to the hazards of having an increasing number of cesareans. And, yes, predictions of birth weight aren't very accurate. Predictions that the baby will weigh more than 8 lb 13 oz (4000 g, the usual definition of "macrosomia") do only somewhat better than flipping a coin. 

(By the way, inducing labor for suspected big baby isn't a good idea either. It doesn't improve outcomes, and it increases the cesarean rate. Inducing women having VBAC labors has also been shown to increase the repeat surgery rate, and a number of studies have shown as well an increase in scar rupture over labors starting on their own.)

I am sorry to say that you may be caught between a rock and a hard place. A number of studies have shown that when an ob thinks the baby is too large, the mother is much more likely to have a cesarean than when the baby actually is large but the doctor didn't suspect it. The ob's belief that the woman will ultimately require a cesarean colors judgment. So, for example, research shows that women who had prior cesareans for lack of progress (not your case, but the principle is applicable) were given less time in labor than women who had cesareans for other reasons. It is also true, unfortunately, that many doctors who start off by saying that they will honor a woman's right to VBAC start finding more and more excuses to push repeat cesarean as the pregnancy advances. "The baby is going to be too big" is one of them. Your saying that your doctor told you that repeat surgery was your only option with a big baby suggests this may be the case with your ob. Any competent adult under any circumstances always has--or should have--the right to refuse surgery. Your ob's casual assumption that this is not the case raises a red flag. But if your doc is trying to talk you out of a VBAC, so few obs are doing VBACs that you may not be able to find someone else to take you.

I suggest you find out more about your ob's attitude toward VBAC. Ask what percentage of your doc's patients with prior cesareans plan VBACs and of them, what percentage have vaginal births. You should hear a reasonably high percentage of women opting for VBAC. If it's only a few percent, it means your doc is discouraging them, setting unreasonable restrictions, or both. And of the women who plan labor, 3 out of 4 should have vaginal births. Numerous large studies have shown this is achievable in a general population. If the number is much less, your doc isn't trying hard enough. I also recommend you surf the International Cesarean Awareness Network website. They will almost certainly have content that is helpful. 

-- Henci