There may be several things that you have in common with your birth mother and other things that are completely different. Cultures, values, religions, hobbies as well as a multitude of other things are all part of what makes a personality. The person whom you are about to meet may have very different opinions and values than you do. Keeping an open mind is the best way to prepare for any differences in a reunion. Another point to consider is that your birth mother may have married and had other children.
Most birth mothers do go on to have families.
Thinking about the possibility of meeting a large extended and immediate family is something to consider. In some cases it is difficult to meet other members of the birth family if your birth mother has not yet told anyone about your birth. Giving your birth mother time to discuss the reunion and the impact that it may have on members of her family is usually the best solution. For families that have known all along about the adoptee, they may be very happy to meet them and include them as part of the family. It can be overwhelming meeting a large number of people all at the same time.