My OB told me that late scan measurements were NOT accurate, and I know plenty of people who have been told they are having large babies who then go on to deliver one under 8 pounds. There really is no way they can accurately predict weight by this stage, and it makes me angry that they scare people by saying things like that. I had a friend in your exact poisition who opted for a c-section as a result of her fears, and her ds turned out to be 8 pound 2 so not big at all.

Also, remember your body will be better at giving birth this time, so even if baby is bigger than your first there is no reason to think you will not be able to birth it.