Why does most women hemoglobin level drops after having lipo and bbl? What can I do to prevent it from happening?

A low hemoglobin count can be due to blood loss, which is atypical after having lipo and BBL.  In an otherwise healthy person without anemia or other consuming disease, there is usually nothing that needs to be done.   Your PS is in the best position to explain why your levels may drop.

Dear Gorgeous4942,
Every surgery causes bleeding, which can cause a drop of Hemoglobin level. If you are considering a surgery, 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

After any liposuction, there is some blood loss (usually minimal).  Postoperative blood tests (CBC-Complete Blood Count) tests for anemia and several other factors.  Low blood counts found after surgery are the result of small blood loss combined with an increase in fluid throughout the body which can 'dilute' the blood and lead to a diagnosis of anemia (low blood count).  There is nothing to be afraid of unless your blood count is low going into the procedure, or if you had unusual bleeding during the procedure.  If you are asymptomatic (no shortness of breath, increased heart rate or low energy) then you should be fine with eating properly and if concerned, taking Iron and Vit C.Dr T

Hemoglobin levels can drop from 1 to 3 points following 360 lipo and BBL. This is why we advocate that your starting hemoglobin be at least 13 on your preop labs prior to undergoing high definition liposuction. Please consider a virtual consultation with a high def provider to appreciate how you can avoid unnecessary blood loss by avoiding blood thinning foods, medicines, and supplements.

hemoglobin and hematocrit levels will drop from blood loss which happens during surgical procedures.
There can also be changes due to chemo dilution or Volume deficit’s.
Typically Liposuction with or without fat transfer procedures if done with good surgical technique have little blood loss.
Rarely more than donating a unit of blood.
A red blood cell has an average lifespan of 120 days and I replaced fairly frequently.
The body will be stimulated produce more red blood cells from blood loss and usually compensates quite quickly.Changes in hemoglobin or hematocrit levels from surgery is not gender dependent.
Best, 
Mats Hagstrom MD