Can I go from a DD to a B cup?

Unfortunately, you have not told us your bra size. If you are a 32 or 34 each 100 grams
corresponds to 1 cup size change. If you
are a 36 or 38 each 200 grams corresponds to 1 cup size change. From this, you can compute the weight required
to reduce you from a DD to a B. However,
there is a new technique called The Ultimate Breast ReductionTM. This technique transfers the weight of the
breast to the underlying muscle allowing the patient to keep the breast size
proportionate to their body and eliminate pain.
This technique avoids the ugly vertical scars of the traditional
technique, maintains nipple sensation and the ability to breast feed. You are not obligated to go to a size B to
relieve your symptoms using this new technique. Best Wishes,Gary Horndeski, M.D.

Breast reductions cannot guarantee a specific cup size, and there is no a "size limit" per se. The goal of a breast reduction is to reduce the breasts to a size and shape that suits your frame, and helps alleviate your symptoms. That being said there is a range of sizes or reductions that can be done safely, so it is useful to know what you prefer. If you truly have a small or narrow frame, a B cup may suit you just fine. It is hard to say without seeing you in person, but most surgeons would not guarantee a cup size anyway, because the volume is not the only important thing to consider when getting a breast reduction. The shape also matters, so sometimes your surgeon may go bigger or smaller as needed to maintain the best shape. If you are having physical symptoms such as shoulder grooving, back pain, and rashes below the breasts, and you have tried conservative measures and they have failed, it is possible that insurance can cover some of your costs. I would recommend consulting with a board certified plastic surgeon for a consultation in person.

but you will have smaller breasts.  If you let your surgeon know, he/she can be aggressive and make you as small as possible at that time.  Heal and then you can decide with your surgeon if any further reductions could be accomplished.

It can be very difficult to reduce a breast to a "B" cup from a "DD" without sacrificing shape. Remember that the tissue that carries your nipples and maintains viability of the skin flaps has to be of a certain minimum thickness as well without compromising the survival.