Pregnancy is very hard on a woman's body and often has a lasting impact on her health. I'm writing from experience as I am a mother and grandmother.
We, men and women, are not fully mature in our bodies and minds till we reach our twenties. So pregnancy and giving birth are doubly traumatic and can lead to doubly serious and long lasting health problems for adolescent women. This is evidenced in some of the Third World countries where teenage marriage and pregancies are the norm of a part of the population. The complication and death rates from pregnancy are magnified for this portion of the population.
As a mother, any time I hear of a child bringing a child into this world, I want to cry.
So you mothers and fathers out there, please don't do what the Palins did. Do make sure your sons and daughters are fully informed in the means of birth control. Then if you also want them to be abstinent, advise them on that too, but at least they will be protected. It works! For instance, the teenage pregnancy rate in Holland where birth control is taught in schools (in Phys. Ed!) is practically nill, and so is the abortion rate.