What EXACTLY is conception?

The Medline Plus Dictionary has an ambiguous and contradictory definition of conception:

"the process of becoming pregnant involving fertilization or implantation or both"

I thought that in the year 2008 we clearly understood that fertilization and implantation are two distinct, separate events! Fertilization occurs when the sperm and ovum unite and implantation occurs several days later after the zygote has divided into a hollow ball of cells called a blastocyst and implants on the uterine wall. So which is it? Does conception start at fertilization or implantation? Apparently the definition got altered from conception=fertilization to conception=implantation by the American College of Obstetrics and Gynecology and the Food and Drug Administration in the early 1960s. Check out the links below for more information on the changing definition of conception and its implications.

Why the ambiguity? According to Albert Rosenfeld, the mixed definition had everything to do with the rise of contraception use.

"Because these substances do not prevent the sperm from penetrating and fertilizing the ovum -the classic definition of conception - they are not strictly contraceptives. What they do is prevent the newly fertilized egg from implanting itself in the uterus. Since the interference occurs after conception, some hold that such practice constitutes abortion. A way around this impasse has been suggested by Dr. A.S. Parkes of Cambridge: Equate conception with the time of implantation rather than the time of fertilization - a difference of only a few days."

Brilliant! Change the meaning of conception and suddenly all forms of birth control that act up to implantation are known to the general public as being benign "medicine." IUDS, the pill, the morning after pill, and Norplant are now in full use without thought of their real effects.

Guided by my beautiful Catholic faith, I am fully against the use of any artificial contraceptives, because of their biological and spiritual effects. Not only do they have the ability to kill a unique, unrepeatable life after it has been conceived, but they keep us closed to the life-giving power of God. They cheapen sex and reduce our committed relationships to matters of convenience and pleasure.

For more information...
The Beginning of Life and The Establishment of the Continuum
American College of Obstetrics and Gynecology Changes Definition
Contraception Deception: The Abortion Rights Movement Plays Word Games to Hide Abortion
Informed Consent and the redefining of conception: a decision ill conceived?

I invite your comments. Why is birth control so widely accepted today? What do you think about the changing meaning of conception? Is it a political ploy or a scientific advancement?