Yes, definitely! When I was pregnant and had GDM, there were a few 100+ degree days, and I didn’t have an air conditioner at the time (yes, I know, it was dreadful). While I did try to stay as cool as I could (drove around in an air-conditioned car, stood in front of a good fan, ate ice cubes, etc.), I did notice that my blood sugar levels SKYROCKETED. Someone on my diabetes treatment team told me that I should expect to have to pre-bolus a lot more on exceedingly hot days than otherwise. Not sure if this just applies to pregnant ladies, or to everyone diabetic in general, but that was my experience.