The September 3rd Health section of the New York Times ran a long article on the growing trend of preimplantation genetic diagnosis, or P.G.D. During the blastocyst stage of her development, two-year-old Chloe was preselected by her parents for implantation.

By subjecting Chloe to a genetic test when she was an eight-cell embryo in a petri dish, Mr. Kingsbury and his wife, Colby, were able to determine that she did not harbor the defective gene. That was the reason they selected her, from among the other embryos they had conceived through elective in vitro fertilization, to implant in her mother’s uterus.

The article mentions that, although this procedure has been used for the last decade "to screen for genes certain to cause childhood diseases that are severe and largely untreatable," it is only recently that couples have begun using it to screen for less certain afflictions.

Couples like the Kingsburys, by contrast, face an even more complex calibration. They must weigh whether their desire to prevent suffering that is not certain to occur justifies the conscious selection of an embryo and the implicit rejection of those that carry the defective gene.

Is this so very different from the decision to use embryos for stem-cell research? If so, where do we draw the line? What do you think?