Santorum's recent comments on the evils of prenatal diagnostics, especially the amniocentesis, has definitely spooked a lot of people, myself included. Besides turning out to be a Pat Buchanan-esque moralist (and one of the few Republicans who could possibly try to pull off Carter's "malaise" speech), he has also demonstrated a particularly dark view of human nature. Prospective parents don't get the batteries of tests, including the amniocentesis, to figure out whether or not to have an abortion but just to check to make sure their baby is okay. Having dealt with both successful and unsuccessful pregnancies, I have to say that I have wanted to have a sonogram attached to my wife's belly 24/7 so I can check up on the baby, due to my delusion (though I don't think I'm along on this one) that if something is wrong there is something we can do to fix it. In other words, parents like performing the prenatal diagnostics because of the positive attribute of trying to protect our unborn children, with physician-assisted abortion the furthest thing from our minds (spontaneous abortions i.e. miscarriages are unfortunately constantly on them).
Also, I think that if Santorum's goal is to have more babies born than less, his argument might be self-defeating. Now let's say that he is elected President and through his moralizing he is able to vilify the amniocentesis so much that it is no longer offered to prospective parents (I realize that is unrealistic but I think that when judging a Presidential candidate you should consider what would happen if they actually could impose their views on society). How many couples deemed "at-risk" due to maternal age or because of family history might decide to forgo having a child altogether? Right now, about 14% of babies are born to mothers who are 35 and over, while only 4 out of 1,000 pregnancies are terminated because of prenatal diagnostic results. In other words, a small percentage of "at risk" mothers changing their minds about having kids due to a fear of the unknown could swamp any benefits that Santorum thinks he would see through less prenatal testing.
Deciding to have a baby can be a tough decision, it doesn't seem to make sense to do something that could tip the scales the wrong way.