I often tell my patients that the most important consideration is how likely are you to maintain the weight loss after surgery. I find that weight loss or gain after surgery is much more likely to affect the longterm surgical result, compared to any weight loss prior to surgery.
Bottomline, try to lose the weight prior to surgery, but try to maintain realistic expectations of keeping it off.
I wish you a safe recovery and amazing result!!
Web reference: http://www.drpaulgill.com