When we explain and defend the sanctity of life, we usually use the word "conception" to mark the beginning of life. Life is sacred "from the moment of conception to the moment of natural death," we say.
But it may be time to fine-tune our language.
By "conception," we normally understand "the union of sperm and ovum." A term also used to describe that event is "fertilization." Indeed, the lengthy hearings that took place in the US Senate in 1982, and the two-volume report on the Human Life Bill being debated at the time, used the terms "conception" and "fertilization" to mean the same thing. (See Human Life Bill, US Senate Committee on the Judiciary, Subcommittee of Separation of Powers, 97th Congress, S-158, April-June 1982, Serial No. J-97-16).
Yet efforts have been made over the years to use the word "conception" to refer not to the fertilization of the ovum by the sperm, but rather to the implantation of the blastocyst (the newly developing human at about a week after fertilization) into the uterine wall. Hence one reads in OB & GYN Terminology, "Conception is the implantation of the blastocyst. It is not synonymous with fertilization" (E. Hughes, ed., Philadelphia: F.A. Davis, 1972).
What's the importance of this? It re-defines pregnancy and abortion. In other words, if pregnancy or conception does not start until implantation, this gives some the excuse to call the killing of a new human life in the first week of its existence "contraception" rather than the name it deserves, "abortion." In law, statistics, and public relations efforts, such a move can mask countless abortions.
A good example is the following quote from the website of Planned Parenthood:
"According to general medical definitions of pregnancy that have been endorsed by many organizations including the American College of Obstetricians and Gynecologists and the United States Department of Health and Human Services, pregnancy begins when a pre-embryo [*] completes implantation into the lining of the uterus (ACOG, 1998; DHHS, 1978; Hughes, 1972; "Make the Distinction…" 2001). Methods of contraception, including emergency contraception, prevent pregnancy by inhibiting ovulation, fertilization and/or implantation (ACOG, 1998)."
Beware of this interplay of words when you hear someone talk about "preventing conception."
With modern technology, genetic manipulation, and the threat of cloning, there can even be problems with the word "fertilization." Yes, human life begins with the union of ovum and sperm. But now, some human lives may begin by other methods of asexual reproduction and the transfer of cell nuclei. And if a person were ever cloned, he or she would still be a person, with full human rights and dignity.
To avoid any confusion, then, about the full humanity of our youngest brothers and sisters, it may be well to adopt the language that "human life is sacred, and is to be protected, from the single-cell stage." This would clearly exclude the interpretation of "implantation" as the start of life, and would include every new human life, no matter how that single cell came about.
* There is no such thing as a "pre-embryo."