Hi Fairytale,
The doctor might mean alpha thalassemia, as Sharmin suggested. If that is the way it is described, beta thal would be stigma B and alpha thal would be stigma A. The reason the doctor is concerned is because sometimes when beta and alpha are combined, it can lead to thal intermedia, but never major. If it turns out that your fiance is a carrier of alpha, then it may be best to try in vitro fertilization to become pregnant so that the embryos can be screened for thal. Sometimes with thal majors, IV fertilization is the method that will be best for getting pregnant anyway, so it might be something for you to think about.
Please don't feel that you offended anyone. You have brought up an important topic. Thals around the world have often had to hide their condition because of the social stigma and one of the purposes of our group is to help change that. Thals should be accepted by society and never stigmatized and by our efforts we change this a little bit at a time.