The answer is yes.....and sometimes no. This horribly unhelpful answer is the truth in part because of how hard it is to define the term natural. Like beauty, a perfectly natural result is really in the eye of the beholder and therefore essentially a relative term. What may be considered a very perfect and natural breast augmentation result for one person may be viewed as poor and quite obviously unnatural to another.
With that disclaimer aside there are a number of ways a breast augmentation can be made to look as natural as possible.
In general the smaller the implant chosen and the larger the patients' starting breast size, the more natural the end result will be.
This is explained by the fact that following a breast augmentation the final breast size and shape is determined by a combination of the implant and the patients' own breast tissue. In a woman with an A cup breast size and a 500 cc implant roughly 90% of the final shape and size is from the implant. This is highly unlikely to ever look "natural"- it doesn't mean someone won't like and even desire that result, it just means that if you asked 100 people if this looks natural, the vast majority would likely say no.
Conversely in a woman with a C cup breast size and a 275 cc implant roughly 25-50% of the final result is from the implant. This outcome will be far more likely to pass for natural in the eye of the general public.
This concept is an over-simplification of the factors at play but certainly an important one to consider for any woman thinking about breast augmentation.
Besides implant size, you and your plastic surgeon need to make choices about the implant shape, location of the implant (behind or in front of the muscle), and of course your overall goals.
Some women express the importance that nobody will be able to tell that they have had breast augmentation. Others would be saddened if even one person couldn't tell the difference following surgery. Being clear about where you lie on the spectrum between hidden from all but your partner to a result that is obvious from 100 feet away, is paramount to your satisfaction with the end result.
In terms of implant location there are two options. The implant can be placed in front of the muscle (and therefore directly behind all the breast tissue) or behind the muscle. One myth that is often heard is that it is always more natural when the implant is put behind the muscle (this being the pectoralis major muscle which sits underneath the breast). This is NOT necessarily true. The main benefit to putting the implant behind the muscle is to provide one extra layer of coverage to minimize the risk of the upper half of the implant being visible. This includes minimizing the risk of visible rippling of the implant. In patients who do not have enough of their own tissue in the upper half of their breast (typically patients with an a cup or small b cup) then placement behind the muscle is advisable. However in patients with sufficient tissue a more natural appearance may be achieved in front of the muscle.
This is because when implants are placed behind he muscle there is a chance that the muscle may pull the implant higher than would be the desired location. Secondly implants behind the muscle will temporarily shift to the outside when the pectoralis muscle is contracted. This is called implant animation and although it shifts back as soon as the muscle stops contracting it can be very obvious at the local gym and can therefore be very unnatural.
Lastly there are two main shape categories to breast implants. There are round implants and shaped implants (also known as tear drop or anatomic). The shaped implants have more projection at the lower half than the upper half to mimic the shape of a natural breast.
Most people would have a hard time arguing that round implants are more natural than shaped implants but it could be also said that the shaped implants are not for everyone. There are many patients whose primary goal is to fill out the upper half of what feels like an otherwise empty or deflated breast. This is of course, by definition, is not done as well with shaped implants and so clearly this is not perfect choice for all patients. Round and shaped implants come in a multitude or projections which is defined as the distance it pushes the breast away from he chest wall.
Similar to the size of the implant argument, the flatter the implant (less projection) the less obvious and therefore more natural the appearance of the result. Conversely, the higher the projection, the more obvious and less natural the result.
From the plastic surgeon's perspective, all of the above issues must be reconciled with the fact that the demographics of women seeking breast augmentation is tremendously diverse. This includes a broad age range 18-75 (yes even in 75 year olds), starting breast size (A cup to D cup), patient weight, breast shape, skin and tissue elasticity, and the list goes on.
For many woman the ultimate goal may just be to have a breast augmentation that allows them the opportunity to both flaunt it and conceal it depending on the occasion or mood. This way depending on what clothing choices they make, they can teeter between obviously enhance and beautifully natural.