5'3", 125 lbs, petite frame. Sientra sizing question - 290cc or 330cc? Or won't it matter much?

Thank you for the question. Actually, on a smaller framed patient, 40 cc difference can be quite noticeable. As you consider breast augmentation surgery, the most important decision you make is NOT size/profile of breast implant, but selection of plastic surgeon. 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.  Again, have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining which operation and/or 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. I have found that the use of words such as “natural” or "B or C cup" etc 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.   Therefore, I ask that my patients not base their communication preoperatively OR  their satisfaction with the outcome of surgery postoperatively, on achieving a specific cup size. The use of computer imaging may be very helpful during this communication phase.
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.  The use of temporary intraoperative sizers, viewing the patient's breasts in the upright and supine position, are very helpful during the breast implant selection process.
I hope this, and the attached link (dedicated to breast augmentation for petite patients), helps.  Best wishes.

I do not think your size range will result in a large size difference in clothing.  I do think it will be a small difference without clothing.  It is much better to accurately discuss implant volume with an in office exam and detailed measurements. In order to make an accurate size recommendation, I would need to assess your chest wall and breast mound measurements/characteristics. I use these measurements to help me during the sizing process to guide you to a safe result for your chest wall and just as important, one that meets your end desires.The next step is to try on this range of implants in the office with your doctor. The key to this success is showing your surgeon the body proportion you desire with a bra sizer and allowing your surgeon to guide you to the right implant. It will be much easier to communicate in implant cc's than cup size when determining the appropriate implant for you during the sizing process. In addition, review of photos and use of rice bags can be very helpful to the patient and surgeon in achieving a safe and happy result. Close intereaction and involvement from your surgeon during this process can help alleviate the anxiety and fears of choosing the right size. I wish you a safe recovery and fantastic result.Dr. Gill