My BWD is 13.5 and 14. If I choose an implant that is 13, will this leave me with an unnatural gap?

Hello and thanks for your question.There are several factors that are very important in determing the shape:-Pre-operative shape-Pre-operative dimension and diameter of the breast-The amount and quality of breast tissue and skin-Implant size, shape and profile-Careful dissection of the pocketIn our office, we use actual implant in the pre-operative period to determine the size.Best Wishes,Dr Sajjadian

Thank you for the question. Careful breast implant pocket dissection and careful selection of breast implant size/profile will be necessary to address your concerns about the space between the breasts. Of course, there may be some anatomic limitations as to how closely the breast implants can be placed, without risking breast implant malposition complications. In regards to specific size/profile of breast implant, despite good intentions, online consultants will not be able to provide you  with  meaningful specific advice.  Ultimately, in person consultation with well experienced board-certified plastic surgeons will be necessary. Careful measurements, dimensional planning, and careful communication will be key.
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.  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 "small D cup" or "fake" 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.  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, helps.

Here's how to understand this issue. A breast implant in cosmetic augmentation is just pillow volume and does not change the basic characteristics of your breasts. It just fills them out and makes the characteristics you had look bigger. The gap between your breasts should stay the same with a properly fitted and positioned implant. The depth or steepness of the sides of the gap will increase but the gap should stay the same. To alter this gap with an implant risks distorting your breast like a foot that's too big for a shoe. You may get away with it but it risks distortions and problems that are hard to revise/correct particularly on attempts to narrow the gap between breasts on the medial sides. Expanding the lateral edge is easier but too much and the nipple-areola will not be centered properly.If your breasts are about 13.5 cm in width upright and with arms down, you need an implant (round, smooth surface) that is about 3/4 to 1 cm less than that to properly fill out your breast width so that it is not overfilled or under filled. The difference is made up by skin and fat. (This does require correct development of the pocket for the implant and positioning the implant properly in relation to the base of the breast). If the implant is properly fitted to the base width or your breast and positioned correctly, the gap between the breasts will stay the same, look natural, and the degree of increase of slope on the medial side has to do with the profile or forward volume of the implant. The lowest profile in saline-filled or silicone gel-filled implants should make your breasts look about one cup size larger. The highest profile implant with the same diameter should make your breasts look about two cup sizes larger. The middle or medium profile would make you look 1 1/2 cup sizes larger, all with the same gap between the breasts but in different degrees of steepness of the medial edge. I would add that it's not a good idea to think that a cosmetic implant can make your breasts look like someone else's or that external sizers are a good way to judge fitting or postoperative result. You're on the right track. Think properly fitting the diameter (and height) of the round implant to the width of your breast at the base and then choose a profile to increase the look of your breasts 1-2 cup sizes. The rest is up to the surgeon to get it positioned in the proper pocket and for you to help get it healed there postoperatively. 

Although base diameter of your breast implant is an important measurement the surgical technique that your plastic surgeon will use to create your breast implant pocket is equally important to avoid a large space between your breasts.Generally speaking and anecdotal estimate is that 200 cc of breast implant will enlarge the breast by 1 cup size from the bra that you are currently wearing.  The implant sizes that you have chosen will likely create the appearance that you want.For more information on choosing breast implant size please read the following link:

Your doctor should be choosing the best implants for you based on the look you want and on your base diameter. Unless this is done properly you could get that gap called Death Valley.

Have 3 doctors measure your BWD and you'll probably get 3 different numbers. It is somewhat subjective. !3cm is probably OK but no real way to tell without an exam. Ask your surgeon who is familiar with your anatomy.