Wearing Bra After Breast Augmentation by Fat Transfer?

     You do not want to damage the fat, and I would agree with others that swelling is usually present at 6 weeks.

The best person to ask is your plastic surgeon who performed the procedure.  He or she intimately knows the surgery that they performed and can steer you in the right direction for your postoperative recovery.  Fat transfer to the breast is living tissue that is moved from one place on the body to another.  The fat needs to establish a blood supply once it is transferred so that it can survive.  This is done by immobilizing the fat with a bra that gives support, but not too much pressure.  Often, surgeons recommend wearing this type of postoperative garment for 6-8 weeks after fat transfer.  If you wear something too tight in this early postoperative period, it can increase the possibility of fat necrosis or fat death.  The best course to follow is to listen to your plastic surgeon.  

As I trust most will advise, your surgeons instructions are most appropriate. The rationale for a loose fitting brassiere is so an not to interfere with the "take" of the fat grafts. Too much compression may decrease the blood flow to the breast and may compromise your outcome. There are probably no studies to precisely define the timing at which there is no potential for harm. 

Thanks for your question, best wishes. 

I think the best person to ask when you can wear a tight bra would be your surgeon who performed the fat transfer.

Thank you for the question.
Although I think online forums can be a good source of general information, I also think that it is best for patients to follow their own plastic surgeon's recommendations. Otherwise, the advice you receive online is nonspecific and  potentially confusing etc.
Remember, that you chose your plastic surgeon for a reason and that he/she is ultimately responsible for your care.
Best wishes.