Conception vs. fertilization.

Commonweal's coverage of stem-cell research on cloned human embryos has generally been fair, accurate, and appropriately nuanced. In your June 17 editorial, "Misleading Photos," however, one important nuance was missed, namely, the distinction between "conception" and "fertilization." Although these terms are often used interchangeably, even in papal documents, "conception" refers to the beginning of a pregnancy within a woman's body, when the embryo is implanted within her uterus several days after an egg is fertilized. In contrast, "fertilization" refers to the process by which an embryo is formed either in vivo or in vitro through union of egg and sperm. (Cloned embryos are not formed through union of egg and sperm.) Infertility practitioners and some people who are publicly opposed to abortion (for example, Orrin Hatch) support stem-cell retrieval from in-vitro embryos on grounds of this distinction, arguing that new life begins at conception or at the onset of pregnancy. The Catholic position should be clearly stated as one that opposes termination of the life of any fertilized egg or embryo (even if the latter has been cloned) regardless of whether conception has yet occurred.

MARY B. MAHOWALD

Chicago, Ill.