Nearly all of the state and federal laws that treat embryos as persons contain a fundamental ambiguity. Contrary to common belief, there is no "moment" of conception. Instead, conception is a forty-eight hour process, during which the haploid genomes of the sperm and egg are gradually and precisely transformed into the functioning diploid genome of a new human embryo. During that two-day period, many common clinical and laboratories activities take place, including the culling of unsuitable embryos, the freezing of others, and the testing of embryos for genetic abnormalities. The legal status of these activities will turn on the point in the two-day process of conception that is chosen to trigger the life-begins-at-conception laws. In this article, I argue that laws triggered by conception should not take effect until the process of conceiving a new diploid embryo is complete. This occurs when the embryonic genome begins to function, roughly forty-eight hours after insemination, at the eight-cell stage. Prior to that, a new human life is being conceived, but has not yet been conceived. Although many people will find this a surprising conclusion, it is consistent with both the gradual nature of the transformation from gametes to embryo and with the goals that the authors of these laws sought to accomplish.
Philip G. Peters Jr., The Ambiguous Meaning of Human Conception, 40 U.C. Davis L. Rev. 199 (2006)