Teens who know that their parents will be notified might not be so quick to have an “unwanted” pregnancy.”
Sometimes it’s the other way around and the parents don’t want the teenager “saddled with a child” so force the teen to have an abortion. Teens may know the only way they can keep the child is if her parent’s don’t know.
Either way, the teen's behavior will still be influenced by the desire to hide her activity from her parents. There are a lot of variables in this, but the bottom line is that teens are reluctant to let their parents know they are seeking an abortion. So parental notification laws will almost certainly cause a drop in "unwanted" pregnancies.