I purchased a Small in these leggings because most reviews said they run true to size. I've had both a medium and small in Old Navy's cotton maternity leggings, and the small fit me best, while the medium became baggy around the butt and thigh area. So I expected these to be a good fit in size Small... as well. But... they are much more snug. I just got them in the mail today, and almost immediately tried them on. The fabric seems to be of good quality and the navy color is true to the pictures, but I kind of wish I'd gotten a Medium. (for reference I'm 5'4", 145 lbs at 20 weeks) If you're looking for something to "hold you in", then I would go with your regular size. But if you want a little breathing room then I would size up. I'm hoping they'll stretch some as leggings sometimes do. Otherwise they will probably make a good post-partum pair to wear for the first couple of months after baby.