I had a BBL, 1100cc in 2014, then 2015 2nd round but just for filling in dimples.

Buttock shrinking after a BBL can be related to several things. Firstly, non-viable fat cells could have been injected (this is seen when laser liposuction is used to harvest the fat, or poor harvest technique is used). Second, injection of other "non-fat" material, such as tumescent fluid (this can be avoid by removing all this liquid with spinning). Thirdly, poor injection technique that causes injury to the fat cells, which subsequently die. Fourthly, too much post- op pressure on the fat cells as they are growing their own blood supply. And lastly, factors that are unknown and related to your body's ability to heal.  Without knowing exactly what was done during each of these steps, it is impossible to tell your where the problem was. The key is to find a surgeon who is experienced in BBLs and can show you photos of his/her own patients many many years out from surgery, not just immediate "afters" taken on the operating room table. Good luck. 

Ideal candidates are at a stable weight,  in good health , and have excess fat in some parts of the body and too little in other regions.  Gaining weight before the procedure is to no advantage and when you lose weight again the fat cells will shrink just like the donor site fat cells.  Typically, the transferred fat results in a significant increase in volume of the body site being treated.

Thank you for your question.There are many things that can affect BBL.  First you should expect a reduction of 30-40% of the fat transferred to the buttock.  Then there are other factors that are involved:!.  How the fat is harvested (taken out)2. How it is prepared3. How it is injected4. Where it is injected5. Post operative care of two weeks of no prolonged direct pressure on the buttock.6. if you have had weight loss or gainSo without truly knowing all this it is hard to say exactly what is going on, thus your best resource would be your plastic surgeon.