underwear size.

Okay so VS is doing an 8 for 27$ panty sale tonight, but I was thinking am I gonna need a size bigger for the next couple months? Did you guys grow more in that area? My breasts are def. getting bigger but I don't want to buy my size and grow out of them. But I also don't want to get a size bigger and not fit them, or losing all that weight after the baby comes. What are your stories with weight gain in the thigh/butt area? lol weird question I know. But I love my VS panties