An appropriate compliment to a recently postpartum mother is, "You look great!" If you don't think I look great, you don't need to tell me that.
An inappropriate compliment is, "Considering you just had a baby, you look great!" No. NO. It's a backhanded compliment. Either I look great, or I don't. The fact I recently had a baby is irrelevant.
Another inappropriate compliment is, "You look like you've lost almost all of your baby weight!" Again, NO. I've lost ALL of my baby weight, plus some. My belly is not poochy, and I can comfortably wear clothes that were snug before I got knocked up.
I'm going to remember the people who keep telling me these things and eventually, I'm going to tell them one of the following:
"Considering you're about 20/30/50/200 pounds overweight and eat too much junk, you really look fantastic!"
"You look like you've gained weight since I saw you last!"