Amniocentesis (sp?) can diagnose many conditions with absolute certainty. If you're interested, go do your own research-- I did mine when I had my children fifteen years ago. (Don't forget-- childbirth itself carries both immediate and long-term risks for the mother, which, however small, must be weighed against the even smaller risk of a mis-diagnosis.) The technology has only gotten better since then. Moreover, for hard-line right-to-lifers, that's ONLY the baby's right to life-- for all they care the mother's can die right and left, no problem. I have a major problem with this attitude.
The way I figure it, God gave us brains as well as hearts and intended us to use both. Sophisticated moral judgments aren't the easiest course, which is exactly why the fanatics aren't willing to make them. That's a serious moral failing right there.