I'm 5'4" and wear a 34D and size small for all other shirts post pregnancy...according to the sizing recommendation, I ordered a medium.  I found it wayyyy too small, and not very stretchy, so difficult to even get on, and not comfortable to wear because it was too snug.  I expected it to be snug, but stretchy (like any other tank top), but because the material isn't very stretchy, it just felt tight.  I made the mistake of removing the tags and washing them right away, so it was too late to return them.  I'm 1 year post partum at this point, and never wound up wearing these tanks.  I thought it was a great idea, but unfortunately wasn't comfortable enough for me to ever want to wear it.