I don't like hearing weight as a reason for c section... I think it's unfortunate. Those weight estimates are guesses and seem to be off more than they are ever right. Even if baby was 10lbs, many people have vaginal births to 10lb babies. I just don't think that alone should be a reason to have major surgery. Two co workers had 9-10lb babies, my boyfriend and his two brothers were 9-10lbs, the nurse at my Dr office had two almost 10lbs. Just my thoughts
Good luck on the c section, but remember the ultrasound is just an estimate. One of my best friends had to have a c section because the ultrasound said the baby was going to be almost 11 lbs and when she actually had her the baby was barely 6.
It might not be because of the diabetes, my bf was 10lb 5oz at 40 weeks, his mom delivered him naturally but she tore really badly. She didn't have gestional diabetes.