Bridesmaid dress size help

Ashley • FTM 👩‍👧‍👦 babygirl 4/20/19

My due date is April 26. I am in a wedding on May 17. I’m really struggling with what size to get. I can choose my dress any dress in a specific color by a specific designer. I’m looking used since the brand new dresses run $300+. I don’t want to spend that much for a dress I will literally only wear once.

I’m looking for style with higher waists. I would normally buy a size 4. I am struggling with whether to buy a size 6 or 8 or even 10. I’ve gained abt 15 lbs so far @ just abt 6 months. I don’t appear as if I’ve gained too much weight anywhere. I’m wearing jeans still one waist size up than my regular jeans. There 2 options right now on used sites in size 6 and id like to buy now if that’s the size I’m going with, I just don’t want to be stuck buying a bigger size at full price the week before the wedding if the 6 doesn’t fit 😤

Anyone have a similar experience? How many sizes did you go up?