I'm 5'2'' 112 lbs 34A, what cup size will 300cc high profile silicone implants under the muscle take me to?

Thank you for the question. Keep in mind, that there is no accurate correlation between breast implant size use than specific cup size achieved. 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're 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. I have found that the use of words such as  “natural”  or “C or D 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.
 The use of computer imaging technology may also be very helpful during this communication process.

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.
I hope this (and the attached link) help.

At size 34 A each 100 cc’s of implant corresponds to 1 cup size change. 300 cc implants will take you up 3 cup sizes to a D. The profile of the implant is irrelevant under the muscle since the muscle compresses it.

Best Wishes,

Gary Horndeski, M.D.

The selection of cup size is not as precise as one would think. Variables in height, weight, and biodimensional measurements of chest base width, soft tissue constriction, and volumes will preclude an accurate prediction of outcome. Many implant manufacturers provide guides and recommendations based on projection and diameter of implants. However, after all these measurements and considerations are taken, we usually use clinical experience to project a one to two cup size increase for our patients. With the measurements you've shared, I would guess that 300cc high profile implants would give you a rough two cup increase. Hope this helps.