Is 550cc too big for me? I would like to go from a B to a 34DD

 Thank you for the question. 
 Based on your photographs, I think that you are starting at a good place and should have a very nice outcome with breast augmentation surgery.
There are several steps taken to select a specific size/profile breast implant for a specific patient. These steps will vary from one practice to another.  I prefer to have a wide selection of implants (all profiles) available in the operating room. I use intraoperative sizers and place the patient in the upright position to evaluate breast size. Use of these sizers also allow me to select the breast implant profile (low, moderate, moderate plus, high-profile) that would most likely achieve the patient's goals. The patient's goal pictures are hanging on the wall, and allow for direct comparison. I have found that this system is very helpful in improving the chances of achieving the patient's goals as consistently as possible. 
Ultimately, careful communication of your goals (in my practice I prefer the use of goal pictures, direct examination/communication in front of a full-length mirror, in bra sizers, and computer imaging) as well as careful measurements (dimensional planning) will be critical.
Generally speaking, the best online advice I can give to ladies who are considering breast augmentation surgery ( regarding breast implant size/profile selection) is:
1. Concentrate on choosing your plastic surgeon carefully. Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you are looking for. Ask to see lots of examples of his/her work.
2. Have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining breast implant size/type/profile will most likely help achieve your goals. 
In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. For example, I have found that the use of words such as “natural” or "DD cup” etc means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on him who makes the bra; therefore, discussing desired cup size may also be inaccurate. Again, the use of computer imaging has been very helpful during the communication process, in our practice.
3. Once you feel you have communicated your goals clearly, allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals. Again, in my practice, this decision is usually made during surgery, after the use of temporary intraoperative sizers.
In your case, my best advice: more communication. It will definitely worth spending more time (prior to the date of surgery) with your plastic surgeon to discuss further.  As you know, it will be important for many reasons, that you feel comfortable that you and your plastic surgeon are on the "same page" prior to proceeding.
I hope this helps. Best wishes for an outcome that you will be very pleased with. 

I appreciate your question.

The size of implant best for you is dictated by your chest wall measurements.  Once we determine that we can choose the profile based on what you want or need to achieve.  If you are seeking a natural look, then the diameter of the implant should be equal to or, more ideally, smaller than the width of your breast. The breast width is a measurement of how wide your breast is at the base, which should be measured at the level of the nipple. Choosing an implant that is smaller in diameter than your breast width will avoid the "side breast" fullness that is often associated with a more artificial appearance.  Other than that, you should choose the implant based on volume, not on the dimensions of the implant. You should choose a board certified plastic surgeon that you trust to help guide you in this decision.  

Silicone will give you a fullness at the top (upper pole fullness).

Silicone implants come pre-filled with a silicone gel and are the softest implant available. They feel more natural, which makes them a good option for women with less natural breast tissue; but they require a larger incision. It may be more difficult to realize if this type of implant has ruptured, so it is important to monitor them with annual follow-up visits. Additionally, because this implant contains a more liquid silicone (less cross-linked), if this implant should rupture, it will leak only into the scar capsule formed around the implant but may cause some discomfort or implant distortion.

Anatomic gummy bear implants might be a good choice to give you volume.

These highly-sought-after, anatomic implants offer a look that more closely resembles the natural silhouette of a breast, and, therefore, are a very attractive option for individuals seeking a natural-looking, aesthetic primary breast augmentation. Additionally, these implants are an especially excellent option for patients undergoing restorative or corrective breast surgery because they provide more stability, shape, and reduced incidence of capsular contracture. Compared to other types of silicone gel implants, the silicone in the cohesive gel implant is more cross-linked; therefore, should the implant shell “rupture,” it maintains its shape and silicone does not leak.

During your breast augmentation consultation, you should feel the different types of implants available, and try on various implant sizers in front of a mirror to help you to get an idea of how you will look following the surgery. You should also bring pictures of the look you would like to achieve, as well as a favorite top to wear when trying on implant sizers.

The best way to assess and give true advice would be an in-person exam.

Please see a board-certified plastic surgeon that specializes in aesthetic and restorative breast surgery.

Best of luck!

Dr. Schwartz

Board Certified Plastic Surgeon

#RealSelf100Surgeon

#RealSelfCORESurgeon