I'd say so. I just loaded up on a bunch at the outlet in Vegas and normally wear size 6-8 depending on the brand, and most of the size small fits me fine. They carry some different jean brands though, and sometimes I'm a medium in those, but that's normal for jeans to fit weird like they do when we're not pregnant! Don't even escape that when looking for mat clothes!
During my first trimester, I thought I might get away with continuing to wear my low-slung hipster jeans for the duration. And I probably could have eeked them out for way longer than I did, had I invested in button extenders or a Bump Bandeau (as recommended by JTryner in an earlier thread). But there was always going to come a point when I got a little larger all over (be it from swelling, fat or, y'know, the extra 2 ½ pints of blood that swishes around in women when they're growing a foetus).
Ok so I HATE maternity clothes... or I should say hated... I bought my first pair of maternity jeans yesterday from primark of all places and I am literally in love! They are still nice and skinny and fitted but so comfy around my bump - check out my maternity video on what I purchased here; https://www.youtube.com/watch?v=r3bLjGSHMZE&index=3&list=UU-DxGKz7B0xh_zSDzgnL2cw