What are the chances of a baby contracting add if only one parent has add?

Some chance: There is robust evidence of the genetic heritability of adhd. Twin studies and family studies point to a genetic heritability of up to 60%. A sibling of a child with adhd has a 3x increase of risk for adhd.

High: I agree with Dr. Esguerra. Having a parent with ADHD confers a 70% risk . Even if yours was the primarily inattentive type seen in 70% of girls with ADHD, your child could have one of the other types, as well. (S)he won't contract it; it's not contagious. However, good routines, consistent parenting & modeling problem-solving will help modify the expression of the gene(s).

ADHD inherited?: There is a genetic component to ADHD. Some studies have indicated that 1/3 of fathers who have ADHD will have children who also have ADHD. I don't have information on the genetic influence of mothers.