Well, I have never had twins, but my best friend who I am in nursing school did and I just phoned her and read these posts. She had similar circumstances. She measured about 9 weeks further along than she really was. Everyone seems to be under the impression that twins are born rather small, you know, around 4 pounds. Well, she did not have gest. Diabetes, whe was just retaining water and wher boys were born they both weighed around 7 pounds each.
She had her boys here in the Memphis area 11 years ago, but she remembers well what you seem to be going through. Maybe your twins will be born larger than they currently "seem" to measure. Hope everything goes well. And she said not to worry, the docs in this area are really great!