Survival of the fittest has taken on a new dimension, with new advances in the science of modern baby-making.

With progress being made in chromosomal testing, fertility doctors now can single out the best of several embryos created in vitro to implant in a woman?s body so that her chance of having a successful pregnancy is vastly increased.

The testing is done on embyos that are five days old.

Another technique doctors are using to be more certain that an embryo is fit is time-lapse imaging to study the development pattern of the embryo.

Both techniques, the New York Times reported on Saturday, can potentially provide more information than the approach now used to judge an embryo?s fitness, which is to look at it under a microscope.

If clinics can be nearly certain that an embryo is fit,? the paper said, ?they might feel more comfortable transferring only one embryo rather than two or more, as is common practice,? the Times explained. ?That would reduce the chances of producing twins or triplets, which face greater health risks than single babies.?

There are perhaps few groups of people who get more nervous when hearing talk about pre-natal testing than people with Down Syndrome and those who care for them.

In addition to dehumanizing humans at their smallest and most vulnerable stage, subjecting these tiny humans to [pre-implantation genetic screening] places them at the mercy of a decision maker who decides who should live and who should die. Some would call this eugenics,? said Mark Bradford, president of the Jerome Lejeune Foundation, USA. The organization supports research into Trisomy 21, or Down Syndrome, which was first explained as a chromosomal abnormality by French geneticist Jerome Lejeune.

?If the embryo is destroyed because it is found to have a disability, then the selection is at the very least a form of discriminatory infanticide,? Bradford said. ?Inasmuch as it is the destruction of human life (because human embryos are living and what is living is human) in reality embryo selection in its effect is just a way to advance the process of prenatal diagnosis and abortion by several weeks. What begins as a misplaced but well intended act of giving life, ends in the destruction of life because that particular life is seen as undesirable.