Why can't doctors go from D cup to A cup? It bothers me that most breast reductions almost never go small enough.

The best way to determine what your breast size should be with respect to your anatomy and give true advice would be an in-person exam with a board certified plastic surgeon who performs hundreds of breast procedures annually. Not only does proportion depend upon the aesthetic balance of your breasts with your shoulders, waist, hips, and buttocks, but also upon your objectives, active lifestyle, soft tissue quality, muscular anatomy, and long-term concerns. There is also a limit to how small you can go due to tissue that needs to be retained for the nipple/areola to maintain a good blood and sensory nerve supply.

thank you for the question.  If insurance is paying for the surgery they probably require a certain minimum amount removed.  As far as how much the breast is reduced it seems to me that there is more of a risk of over reduction.  After surgery the remaining breast tissue will atrophy to a considerable degree so I tend to leave my reductions on the more full side.  In addition to that, they end up looking better.