Learn the Facts

When does pregnancy begin? At “fertilization” or “implantation”?

Until 1965, physicians considered pregnancy to begin at fertilization, when the male sperm unites with the female ovum in one of the mother’s Fallopian tubes, creating a new human life. Since then, the American College of Obstetricians and Gynecologists has identified the beginning of pregnancy as implantation, when the tiny human being (now scientifically known as an “embryo”) implants in the mother’s uterus and begins to draw nourishment, eight to ten days after life begins.

The reasons for this change are disputed. Some argue the new definition was established to allow intrauterine devices (IUDs) to be characterized as contraceptives rather than abortifacients, since they can inhibit implantation.

But even if one concedes the new definition, the critical question is when a new human life begins, not when pregnancy begins. Once that new life has begun, any measure taken that destroys that life constitutes an abortion.


Browder, Sue Ellin. “When Human Life Begins.” National Catholic Register. December 14, 2009. http://www.sanalbino.org/Files/WhenHumanLifeBegins.pdf.

Willke, John, MD and Barbara Willke. Abortion: Questions & Answers. Cincinnati: Hayes, 2003.

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