What's the difference between maternity underwear and normal underwear?

chizzle91

I'm only 8 weeks, so I don't think I'll really need to worry about this for a while, but I was just curious what the difference was? Looking at clothes online, I couldn't really see a difference, so I was a little confused

 

(I'm sorry if this is on the wrong board, I wasn't really sure where to ask lol)