I had gestational diabetes for my third as well.
I maintained it well with diet. I got to eat a lot of good things. I had to avoid some things completely like sweets, and heavy carbs like bagels.
I felt my diet plan had me constantly eating though. Breakfast, then snack, lunch, then snack, and finally dinner. I think I tested 2 times a day.
It really helped with water weight gain. Before I stated I was very puffy.
My baby was premature, but he was a bit bigger than a 28 week baby. By size they estimated him at 30 weeks. I knew how old he was according to my trusty NFP chart. Doctors finally agreed, his development was that of a 28 week baby.