Pre-natal testing tends to take place late on in pregnancy, beyond the weeks when abortions are usually performed. Any foetus involved is therefore a wanted child. Many choose to have a test for disorders such as Down's Syndrome because they realise that, however much they want the child, the demands of a severely handicapped person are greater than they are able to meet.
You cannot equate such a test with testing for schizophrenia or heart disease, or other treatable conditions. I find it highly unlikely that, even if these tests were available, many would choose to use them, and equally unlikely that, if they were administered and the results were positive, abortion would be the preferred option.
For the overwhelming majority the "perfect" baby is not one with blond hair, blue eyes, a high IQ and a heterosexual disposition, as Bryan Appleyard implies, but a child to whom they are able to give the care and attention it needs.
Scientific research and development is of huge benefit to mankind. Let us not halt this development by our distrust of human ability to make sensible decisions when given the advantage of greater knowledge.