I also have gestional diabetes. I am fortunate that I do not have any other complications. Make sure you get in with a dietician and monitor your blood sugars. I plan on delivering vaginally, I am 37 1/2 weeks and I will be induced at about 39 weeks. Thankfully they keep measuring my baby to be on the smaller side, so I have that as an option. If your placenta is really low, where it is presenting first, they will not let you deliver vaginally and you will have to have a c-section. You will start having regular ultrasounds with the gestational diabetes anyway so they will continue to monitor the placement of your placenta to determine the best method of delivery.
My cousin had gestational diabetes with her 1st and she had a low lying placenta. She had the scan done later in pregnancy and it had moved. So she delivered naturally. She was induced the day after ger due date.