The pedigree diagram for Down syndrome typically lists three generations of family and shows any family members with the disease or indicators of it. Down syndrome is caused by an additional copy of the 21st chromosome.
Since the extra chromosome only shows up in people with the condition, it is very unlikely that there will be indicators in previous generations. The best indicators for someone having a child with Down syndrome is the age of the mother and the pregnancy history of the women in the family. If a family is prone to miscarriages or other types of pregnancy loss like still birth, then they have a higher chance of having a child with Down syndrome.