It would depend on the amount of marrow taken, the expertise of the doctor removing it, the age of the patient and I am sure many more factors. You should inquire when doing your research approximately how many stem cells you will be getting and how they are processed. If they are umbilical cord stem cells, make sure they are certified for purity and are purchased from a reputable source.
For those contemplating treatment in Mexico, please do a Google search for the number of foreign patients injured or killed or harmed in any way while undergoing stem cell treatment in a clinic in Mexico. I don't believe you will find any. Reputable Mexican clinics pick you up from the airport or your hotel and transport you to the hospital or clinic where you will have treatment. The clinics and hospitals are close to the border. I have never felt any unease when I went there, but I am well traveled and realize that my chances of getting mugged are just as great in St. Louis or Chicago as they are while getting treatment in Mexico. It is just not a factor in my decision making, however, I will state that I hate the return border crossing. It can be a long wait. If you can fly, you have many options as far as choosing a clinic. I don't have that option and must drive to wherever I am getting treatment thus I am limited to Mexico and the U.S.