Laws requiring minors to seek parental consent or to notify a parent prior to obtaining an abortion raise the cost of risky sex for teenagers. Assuming choices to engage in risky sex are made rationally, parental involvement laws should lead to less risky sex among teens, either because of a reduction of sexual activity altogether or because teens will be more fastidious in the use of birth control ex ante.
This is reminiscent of the old economist joke:
A physicist, a chemist and an economist are stranded on an island, with nothing to eat. A can of soup washes ashore. The physicist says, “Let’s smash the can open with a rock.” The chemist says, “Let’s build a fire and heat the can first.” The economist says, “Let’s assume that we have a can-opener…”
Then the three of them engage in risky sex. Rationally, I assume.