Yes, it has a great impact. First and foremost it means that you cannot compare your result to the result of other women who do not have the same shape chest. It means that measurements using a tape measure are not likely to tell the whole story. And it has a great impact upon the difference in how you look in a bra/swim suit compared to your look in a blouse or sweater.
One aspect to consider is that the chest ribcage is not the same on the left as on the right. For most women, the left ribs are more rounded outwards and the right are slightly flatter and less prominent. This might be the result of the fact that the heart is on the left, but the exact reason is not known. This often results in the need to use a slightly smaller implant on the left side. But there is a more important consideration, read on.
Picture a women whose ribcage is of typical shape - neither sunken in, nor protruding out in the front. Picture how her chest might look in a bra - and how it might look in a sweater. Now picture the center of her chest sinking inward a little but no change in breast size. In the bra, the breasts will look the same size, whether the chest is sunken in, or protruding outward, so no real difference there, but look at what a big impact changing the ribcage will have on the apparent size when she is wearing a sweater. Even if the breast size doesn't change, the woman who rib cage is more protruding will look much larger in a sweater than the average woman and the one whose ribcage is sunken in will look much smaller in a sweater than the average woman.
What does this mean for the individual woman?
First the woman whose chest and rib cage are very prominent. For her, if she fits a C size, then she will look like a C in a bra, but perhaps look like a D in a sweater. If she chooses the size of implant that makes her look like a C in a sweater, she will only look like a B in her bra.
Now the woman whose chest is somewhat flattened or sunken-in. She will have the opposite problem. For her, if she fits a C size, then she will still look like a C in a bra, but perhaps look like a B in a sweater. If she chooses the size of implant that makes her look like a C in a sweater, she will look like a D in her bra.
If your ribcage shape is either sunken-in at the front, or a little bulging out, you must understand this information when deciding upon the size of implant.
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