I don't have personal experience with GDM and VBAC together, but I think the fact that your gynae is still open to you trying is a good sign that it really does depend on how things progress. It might be worth getting a second opinion from another gynae or even a maternal-fetal medicine specialist, just so you can weigh all the options clearly before making the call. The closer you get to your due date, your baby's size and your glucose control will both factor in, so keeping those monitored closely will really help you and your doctor make the best decision together.