Beginning of Pregnancy Controversy - Definitions of Pregnancy Beginning

Definitions of Pregnancy Beginning

Traditionally, doctors have measured pregnancy from a number of convenient points, including the day of last menstruation, ovulation, fertilization, implantation and chemical detection. This has led to some confusion about the precise length of human pregnancy, as each measuring point yields a different figure.

At its 2004 Annual Meeting, The American Medical Association passed a resolution in favor of making "Plan B" emergency contraception available over-the-counter, and one of the claims in the resolution was that hormonal contraception that may affect implantation "cannot terminate an established pregnancy."

Similarly, the British Medical Association has defined an "established pregnancy" as beginning at implantation. The legal definition in the United Kingdom is not clear. Other definitions exist. The American Heritage Stedman's Medical Dictionary defines "pregnancy" as "from conception until birth." Definitions like this may add to a lay person's confusion, as "conception" in a medical context may be defined as implantation but in lay terms may mean either fertilization or implantation. Whether conception refers to fertilization or implantation would seemingly even impact "established pregnancies" such as an ectopic pregnancy. If conception is defined as at implantation, ectopic pregnancies could not be called pregnancies. However, some medical professionals who oppose birth control, including prominent member of Focus on the Family Walter Larimore, have argued that the medical definition of conception should include fertilization.

Finally, the standard historical method of counting the duration of pregnancy begins from the last menstruation and this remains common with doctors, hospitals, and medical companies. This system is convenient because it is easy to determine when the last menstrual period was, while both fertilization and implantation occur out of sight. An interesting consequence is that the dating of pregnancy measured this way begins two weeks before ovulation.