Aww congratulations on your baby! Honestly, timing varies je, some mums dapat admit letter a few days before, some habis check-up last minute baru dapat, depends on your hospital's system lah. Since you're GDM on insulin, I'd say best call your hospital directly to ask exactly bila they'll give the letter, so you can prepare everything properly, especially since you're planning an admission at 38 weeks. A few of us mums-to-be in my group always tanya direct kat hospital counter or midwife sebab setiap tempat lain prosesnya. Good luck with your delivery!