To measure yourself, start at your belly button and go all the way around. Match your measurement to the corresponding size.
I bought this to help with lower back pain and it has definitely made a difference. I'm in my third trimester and commuting by Subway and the support has definitely eased my lower back pain. It is a bit of an investment, but I haven't found significantly lower prices anywhere else. I haven't used the hot/cold pack yet.
used it throughout 3rd trimester. worked great for providing support to low back. felt much more balanced when walking and didn't need to "waddle". didn't notice much difference with leg swelling or bladder discomfort though. would definitely recommend this though it is a bit expensive (loss of 1 star)
My wife loves this support belt. It really helps take the pressure off her cervix and back. The hot/cold pack is also nice when her back is really bad. It looks kind of funny when you wear it with the hot/cold pack in public as you do see a bulge sticking out of your back, however when worn without it you cannot tell it's being worn. It's completely hidden under clothes, even light weight clothes. Just remember to take it off when you sit down as it starts to get uncomfortable quickly.