The standard dose of IVIG for confirmed SCLS patients is 1 gr/kg in Day 1 and another 1 gr/gk in Day 2 every 4 weeks, based on someone's normal weight.
Some patients cannot tolerate so much IVIG in one (two-day) sitting, so they get 1 gr/kg in one day every 2 weeks. Some are also experimenting with subcutaneous (as opposed to IntraVenous) IG, which is the way children oftentimes get their IVIG. One could envision an adult getting 0.5 gr/kg subcutaneously of IG (ImmunoGlobulins) once a week, for example. This should all be discussed with an immunologist or expert internal-medicine physician.
SCLS patients usually gain weight when given fluids in an ER or ICU hospital setting, but they do not normally gain weight, or keep earlier gains in weight.
If you are putting on and keeping weight, to the point of wondering which weight to consider in the proper dosage of IVIG, then it makes me wonder whether your diagnosis of SCLS is appropriate.
Thererfore, I urge you to have you main doctor contact Dr. Kirk Druey at NIH, email email@example.com to request a consultation AND make arrangements for you to be seen at NIH, in Bethesda, MD, right outside the District of Columbia. Dr. Druey is not only the world's expert on SCLS, but he is also a specialist on Mast Cell diseases, which you wrote on your profile page that you suffer from also. And when/if you are examined at NIH for 2-3 days, Dr. Druey will have you seen by several specialisits in the other diseases which you may be experiencing. And since they don't charge anything -- our taxpayer dollars fund NIH -- it's a lot cheaper than spending 2-3 days at the Cleveland or Mayo clinics.