Is it normal to already lose some volume 1 week post op from a BBL?

The results immediately following surgery will be the largest due to swelling and lack of fat resorption.  The buttocks will continue to decrease in size for the first few weeks.   I have observed that between 4 and 6 weeks the buttocks tend to stabilize in volume.  Usually by 3 months, the swelling is minimal and totally resolved by 6 months.  
Kenneth Hughes, MD, ABPS Board Certified Plastic Surgeon
Los Angeles, CA

Thanks for your question. Healing after liposuction and brazilian butt lift is usually pretty straight forward.  You are likely seeing changes as a result of decreasing swelling.  After surgery there is a predictable swelling process that mostly resolves over two months, when the final result really settles in.  The lateer phase of healing takes place over the 2-3 months after surgery where everything really settles and softens.  It is after this time that we are getting close to the final result, though this varies patient to patient. 

Hello dear!!
Thanks for the question and provided information as well.
After a BBL, only about 70% of the transferred fat cells will survive, so it is normal to see a minor reduction in your buttocks. If you have any concerns, I suggest you to follow up close with your plastic surgeon.
Good luck :)