Why won't my surgeon reduce my breast size to a B cup?

During a breast reduction, the nipple and areola are left attached to some of the underlying breast tissue while much of the rest of the breast tissue is removed.  The tissue left attached to the nipple is called the pedicle, and the length and width of the pedicle depend on the patient's measurements.  If the pedicle is too long (based on your pre-op measurements) or is made too narrow (by the surgeon during the procedure), there can be inadequate blood flow to the nipple and, in a worse case scenario, the nipple could actually die.  When performing a breast reduction, the surgeon takes into consideration the patient's size goals and makes a plan to try to achieve those goals without undue risk of healing problems.  I suspect your surgeon felt that a B cup was unattainable because your measurements require a pedicle that will be bulkier than a B cup breast.  I suggest talking with your surgeon again to get additional information about why they don't think a B cup is possible and if you're not comfortable with the answer you're given, consider seeing another board certified plastic surgeon for a second opinion.

Your question is one of the most common questions asked regarding breast reduction. There is always a compromise over size reduction and aesthetic result.The more one reduces the size of breasts, the more skin and breast tissue needs to be removed and the more the blood supply to the nipple and areola is reduced. Creating a flatter breast is certainly possible but may compromise the aesthetic appearance. Depending on how much you wish to reduce you may wish to consider a breast reduction that involves removal of the nipple areola complex completely and placing it on the new breast  - called a free nipple areola graft.It is important that you are aware of the pros and cons of all these procedures and consult with a PS that can show you different results of his/hers that are similar to you so that you  can make an informed decision as to the best treatment option and you can make an informed decision 

Size after breast reduction is somewhat difficult to predict in many cases, as patients often do not have a clear understanding of what it means to go down to a size like a B cup. Women who are accustomed to very heavy, large breasts or who are overweight may feel their breasts are too small after a reduction, even if the cup size was "agreed upon" (there should never be a direct explicit guarantee of a postop breast size) and matches the bra that the patient can obtain postop. If the volume is inadequate to support reasonable cleavage, and especially if nipple blood supply is compromised, it does no good to have an arbitrary cup size if the breast doesn't generally look good or there are major healing problems from nipple loss. It is easier to further reduce a breast than to add volume back, so your surgeon may be thinking along those lines based on experience.

You should be able to find a surgeon that will work with you on this, especially since you are paying for it.  You already are quite informed about the procedure but aggressive resections can be done to 'approximate' your results.  If you remain larger than a desired B cup, realize revisions will be needed so know your surgeon's revision policy.  If your surgeon refuses to accommodate your desires, there are plenty of others that would be happy to have you as a patient.

Congratulations on your decision to proceed with breast reduction surgery.  This operation tends to be one of the most patient pleasing operations we perform. Based on your question, it sounds like you are already aware of some of the concerns surrounding significant breast reduction surgery. Before undergoing the breast reduction procedure it will be very important to select your plastic surgeon carefully and communicate your size goals with your surgeon.  Most patients wish to achieve a enough of a reduction to help with their symptoms while remaining proportionate with the remainder of their torso. 
With the goal of improving communication with my patients I find the use of photographs of “goal” pictures (and breasts that are too big or too small)  very helpful. I have found that the use of words such as “natural” or “B cup” means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup  size may also be inaccurate.
It is possible to reduce the breasts size very significantly.  The concern with the amount of tissue removed is related to blood flow to the remaining tissue;  if too much tissue is removed in one operation the blood flow to the remaining tissue (including nipple/areola)  may be compromised.   Part of the tissue that is left in place is called the “pedicle"; this segment of tissue is responsible for delivering the blood supply to the nipple/areola tissue. If the pedicle is made too small (in the effort to reduce the breasts as much as possible)  then patient will likely have problems with tissue survival.  
The other concern with overly aggressive breast reduction surgery is patient dissatisfaction  afterwards.  It is not unusual for patients who have lived with very large breasts to want to have as much as possible removed. Care must be taken to be judicious in this removal to avoid an outcome where the breasts  are too small in relation (proportionately) to the patient's other body parts.  Again, it is not uncommon, for patients'  breasts to become smaller ( after the breast reduction procedure) with time and/or weight loss-  breast augmentation may become necessary to achieve the patient size goals.
  I hope this, and the attached link, helps. Best wishes.