I just had to share this. So, when I came home from the hospital from having my daughter, I was actually heavier and puffier than when I went in. I had SO much fluid retention, my maternity clothes didn't even fit and I had to go to the store and buy a couple tops, etc. It's a year later now, and I've lost 20 pounds or so, and am down to a very healthy weight well within my BMI. I was looking for something comfy to wear today so I hauled this big shirt out of the closet and put it on. It was baggy -- except in the shoulders! It's a short sleeved linen shirt, not a lot of give, and it was uncomfortably tight around the shoulders! If I needed any proof that some of my weight is muscle, there it is. I guess a year of hauling around an ever-increasingly heavy baby has had some influence on my body shape.
ETA: whoops! I meant to say I lost *30* pounds, which is a huge amount on my small frame. Apparently being a mom is good for shoulder muscles, but not for math muscles :)