So remember all those carcinogens, the nicotine and the other molecules have to cross across the placental membrane. And as they cross they can cause different types of damaging effects. So they can cause problems within the placenta. Now why is that a problem? Well, that's a problem because the placenta is the organ where nutrient exchange and gas exchange takes place. And if the placenta is damaged, then that fetus cannot actually obtain enough nutrients to develop quickly and efficiently.