I wish you the best of luck, aziela, as your transplant planning moves forward.
You are correct to start asking about fertility issues now. Later could be too late. A number of Marrowforums members have dealt with this issue. If you
search the forums for the word "pregnant" (or "pregnancy") you'll find a number of threads on the topic of fertility.
Freezing and IVF are the options we hear about most often, since transplants are likely to prevent a normal pregnancy in the future, but I think that you need to go over all of the options with the appropriate specialist, and that's not a hematologist or a transplant coordinator. It won't hurt to let your transplant team know that you are concerned about fertility but you need to be working directly with fertility specialists to go over the choices, choose one, and take whatever actions will make it most likely that you can have children of your own.
We never want to hear that a patient of childbearing age was rushed to transplant without those conversations.