You ask a very good question and one that shows that you think about breast surgery in an analytical way. The first thing to note, however, is that there really is no standardization amongst bra types or manufacturers as to cup size. Thus, even without implants, you may find that in some kinds of bras you will be a B cup, while in others you may be an A cup, and still another you may actually fit into a C cup. The idea of cup size is more one of proportion than absolute volume. That is, it is really a measure of the difference between the circumference of your chest just below your breasts and the circumference of the chest at the point of maximal fullness of the breast, say in a young breast, at the point at which the nipple projects out the farthest. The bra manufacturer then takes this difference and creates an average size cup matching those proportions; the problem is that some manufacturers think of that "average" in different ways. With regard to breast implants, each manufacturer has different dimensions for width, vertical height in the case of shaped implants, and projection height for a given volume of implant, and those dimensions will vary between round and shaped implants even within the inventory of the same manufacturer. Thus, it makes sense that, as you suggest, with some anatomically shaped implants, where the maximal projection might be a bit higher than that of a round implant of the same volume, the cup size may be influenced by the type of implant. The problem is that there are also so many other variables that all add up in the end to produce the "actual," or best fit, cup size that you will be after surgery. It is really impossible to predict with certainty how a lady's tissues will drape over a particular implant, or how an implant will "settle" and ultimately project in actuality, and this as much as anything else will contribute to the ultimate size of her bra. It is for these reasons that we actually do volumetric sizing for breast implants preoperatively using specially designed sizers that we can actually fit into a sizing bra and evaluate for such things as proportion and dimension. That way we don't have to rely on cup size or implant volume as a primary concern, rather we worry only about what looks good on your body, and then whatever cup size that winds up being after surgery - with the understanding that that still may vary between bra manufacturers - is what you will be. It's a very practical way to approach the issue, and I think the only realistic way to have any chance at accurately achieving our patients' goals. Your consideration about the differences between shaped implants and round implants is a good theoretical concern, but I don't find that cup size is the major consideration when deciding between shaped and round implants. Shape is. For those ladies who want less of an upper pole fullness or roundness, perhaps a more "natural" shape to the breasts, especially those who have naturally small volume breasts and thin tissues, a shaped implant will probably work best, and then it's just a matter of picking size as I described above. For those who want a fuller, rounder shape to the upper pole and cleavage, a round implant will work best, and again, once that's established, it's just a matter of selecting the size with sizing. In the end, cup size will be what it will be in both cases, but the reality is that in both cases regardless of the cup size, I will be confident that I will have a happy patient because we have already taken a "sneak peek" with the preoperative sizing, and we have a very good idea of what we will wind up with.
