How is it possible to go down in band size? E.g. 34 to 32?

The rib cage doesn't change in size. What happens is that if you wear the bra band tighter (band), it will push your breasts deeper into the bra, which would necessitate a bigger cup to accommodate your breasts. For example, a 36B bra is equivalent to a 34C. The bottom line is that you and your plastic surgeon should decide on a "look" size, not a "cup size." After surgery,  it doesn't matter what cup size you are; all that matters is that it fits. Don't get hung up on letters and numbers. For more information on this and similar topics, I recommend a plastic surgery Q&A book like "The Scoop On Breasts: A Plastic Surgeon Busts the Myths." Best of luck to you.

I don't think that band size can actually decrease.  Bras are just an article of clothing and the sizes are not well regulated.I can see if you lose significant weight that it might change your band size.Best Wishes,Nana Mizuguchi, MD

Dear AFlat,  You raise a good point about bra sizes.  It is important to take in to account the back size and this is unlikely to change following breast augmentation.  It may go up a bit with swelling or down a bit with weight loss, but broadly speaking it should be about the same.Having said that, people often wear the wrong bra size and a 32C would probably fit a patient who was actually 34D. So in your example, the patient may have wanted to be a D cup but then come back to clinic saying that she was only a 32C (having been a 34B), when in fact she should be comparing it with the same back size ie 34D.  The main thing is that the bra fits and is comfortable and not so much what the actual cup size is.  I hope that this brings some clarity to it (although I accept that it is perhaps not the most crystal clear answer!).

This amounts to a difference in the way the person measuring goes about sizing the bra.  Breast augmentation should not affect you in this way. 

 You are correct in that the band size is a measurement of the circumference of the chest wall. Since this is a bony structure it will not change. With a lot of weight loss you can make this circumference smaller. Hope this is helpful.