2 years post op BBL, is there a way to restore the fat without having the procedure done again?

Any fat transferred to the buttock has only a certain percentage of survival, and when you lose weight overall, the cells that were transferred to the buttock also give up some volume.  If you have adequate fat to repeat the transfer, then that will improve the percentage of fat that ultimately stays, but if not, then gaining some weight will refill the surviving cells to where they were before you lost weight.

Dear mayaa17,it is hard to tell for sure without an examination. If you are considering a treatment, I would suggest you to consult a board-certified plastic surgeon. Only after a thorough examination you will get more information and recommendations.Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

Sometimes patients request a second round if they gain or lose weight or want more liposuction. Having the BBL done a second time is an option as long as the patient has enough fat to be transferred. The percentage of fat survival in the BBL the second time should be about the same as the first.   The volume loss occurs over the first 6 weeks or so.  After that period of time the volume remains stable assuming weight is maintained. Consult with a board certified plastic surgeon who performs hundreds of liposuctions and BBLs yearly to discuss your ultimate goals and the best path to achieve them.

Your best option to increase the size of your buttocks without surgery or filler is to gain weight back to the weight you were at when you liked the size. 

Hi. One of the characteristic of the fat cell is that it will shrink if you lose weight or  augment if you gain. There is no way to restore the fat than performing the procedure again. Now after pregnancy you should be evaluated again.International Member of the American Society of Plastic Surgeons (ASPS)
Member of the International Society of Aesthetic Plastic Surgery
25 years experience

Hi and welcome to our forum!
Following BBL, the transplanted fat will usually take on the characteristics of the recipient site. Significant fluctuations in weight will affect the fat grafts just as it would normal buttock fat. It should return at least to a certain extent with weight gain. Significant body changes occur with each pregnancy and also may play a role. 
Best wishes...

Fat cells shrink as you lose weight and grow as you gain weight. I always recommend that my patients are at the weight they are comfortable maintaining before proceeding with the surgery, as weight gain/loss can modify results and appearance. You could consider regaining weight to see if that returns you to your desired appearance. However, pregnancy does modify your body, and it would be in your best interest to have another assessment by a certified plastic surgeon -- you may need a BBL revision to help you get your size back.If you are a good candidate for a Brazilian Butt Lift (BBL) revision, the optimal outcomes are achieved with: 1) use of VASER liposuction to harvest the fat, 2) a closed looped system such as Puregraft to process the fat, and 3) strategic micro-packet transplant technique. These three processes have demonstrated over 95% fat graft take. This means that your results will be stable as long as you maintain your weight. As an official VASER trainer, I am routinely referred unhappy BBL patients. One of the most common reasons for disgruntled BBL patients is that patients are not able to accurately communicate their desired buttocks goals to their surgeons.  A buttocks assessment tool can be an invaluable tool to communicate to your surgeon the exact buttocks size and shape you are desiring. A Skype or FaceTime consultation with a BBL specialist can help you get an accurate recommendation and pricing.
Respectfully,
Arian Mowlavi MD,FACS
Realself 100 Hall of Fame Inductee

Dear Ms Mauaa17, 
Thank you for your story and questions. Unfortunately with out a exam of your tissues I can can only make general comments. I hope find the following helpful.Short answer: to increase Buttock size and shape you will to undergo liposuction and fat injection again. 
The amount of fat that takes depends:
1) the gentle technique of harvest providing the least amount of damage/trauma to the fat cells
2) how the fat is injected
3) the receipent area (good blood supply, lack of previous scars, etc.)
4) postoperative care
5) genetics of the individual 
The process for performing a BBL is the same regardless of the patients weight or fat location:
1) harvest the fat 
2) purify the fat
3) sculpting the buttock:
   a) with precise liposculpting 
   b) with precise fat injection
The final shape of the buttock depends on:
1) your underlying boney pelvic frame 
2) the shape of your buttock muscular anatomy
3) the elasticity (stretchability) of the buttock skin skin
4) the patients desired shape (where fat is injected)
The bottom line: 
1) fat survival as a graft is multifactoral but usually varies between 70-80%.
2) the fat that doesn't survive is broken down, dissolves and is excreted by our body
3) the amount injected fat depends on how much fat there is available to harvgest.
4) the individuals genetic anatomy and elastic properties of the skin will dictate 
and limit attaining certain desired shapes
5) Just importantly the liposuction should be done to "sculpt" other parts of the body to attain a body that is in proportion and attractive. Thus a small amount of fat can go along way or in contrast a large amount may not give you the desird appearance
One can try to gain weight prior to the procedure in hope that the areas you can the weight can be liposuctioned. 
Caveat: all fat that is gained may not be deposited in areas that can be liposuctioned.
I suggest you collect multiple model photos of your desired buttock shape/size and schedule several appointments with experienced Plastic Surgeons who are Certified by the American Board of Plastic Surgery and ideally a member of the American Society for Aesthetic Plastic Surgery (denoting by membership as having met additional criteria and a focus on Cosmetic Plastic Surgery).
My best wishes,
R. A. Hardesty, MD, FACS
Diplomate and Certified by the Am. Bd. of Plastic Surgery
Awardee: RealSelf Top 100
wwwimagineplasticsurgery.com
4646 Brockton Ave
Riverside, Ca 92506
(951) 686-7600