Every circumstance is different, but no teen should be assumed to just give up the baby because this is a deep bond and could aid or ruin each of their lives. The situation needs to be assessed for who is around to help, what the young woman wants to do, and how things will be accomplished before making such a big decision.
In delicate situations such as teenage pregnancy, there is not one mold each and every person can fall into. Many teenagers are unaware of the responsibility, time, and finances required to raise a child, and cannot themselves provide a bright future for that child. In any of those situations, the child should be put up for adoption and be loved by a family that truly appreciates them. Although I think that most pregnant teens would fall into that category, some who have a great support system may provide for that child, and will teach them lessons from their experience that cannot be imitated or matched.