I'm 37+4 with my third baby and was told I had GD after a GTT at 29 weeks. I've been unable to control mine my diet alone, my fasting results have been consistently high so I'm now on metformin and insulin.
There's no set rule that you will need induction/section. It's very much a balancing act between how well you are, how well baby is, what medication you're on, size of baby etc. I've found the consultant to be really open to discussing different scenarios and willing to listen to my views. At the moment mine is happy not to go down the induction route (and I'm keen to avoid it) so I'm being closely monitored. Should the situation change and they do recommend delivery then I'll obviously listen!
Breakfast is often the hardest to control. 2 weetabix might have been ok or a slice of toast but together are probably not ideal. Your body has to work much harder to process 2 types of carb in a meal which sends your sugars high. So, have lasagne but not with garlic bread or curry with rice but not naan bread. Also food in its pure form will break down slower so boiled potato rather than mash.
The dietitian also recommended spreading my carbs out during the day so I wasn't eating loads at one meal then none at another. I'd been having bacon and eggs for breakfast but actually it was better to have it with a slice of toast, a bowl of soup for lunch with a sandwich/oatcakes rather than on It's own.
Snack wise I tend to eat crisps (like Walkers rather than more processed ones like Quakers), fig rolls, digestives, oatcakes, popcorn, raw carrots etc. Some fruit is ok but I tend to only eat it as part of a meal.
It's a lot to get your head round but after a few weeks you get into the swing of it. I'd kill for some cake though lol.