I went through my first pregnancy thinking that if I just bought regular, but larger sized tights that would work. After buying and wearing these for my second pregnancy, all I can say is, "What was I thinking?!?" These are super comfortable, stay in place and are thick.  I wear them all day and forget about them. Ordering my prepregnancy size gives me a perfect fit. I've been wearing them since 23 weeks, am currently 26 weeks along and know that they will fit me through to the end. The Amazon general sizing chart that pops up for this product is no help so I went to the manufacturer's for guidance. Great product!