Controversy over the beginning of pregnancy occurs in different contexts, particularly as it is discussed within the debate of abortion in the United States. Because an abortion is defined as ending an established pregnancy, rather than as destroying a fertilized egg, depending on when pregnancy is considered to begin, some methods of birth control as well as some methods of infertility treatment might be classified as causing abortions.

The controversy is not primarily a scientific issue, since knowledge of human reproduction and development has become very refined; the linguistic questions remain debated for other reasons. The issue poses larger social, legal, medical, religious, philosophical, and political ramifications because some people, such as Concerned Women for America, identify the beginning of a pregnancy as the beginning of an individual human being's life."The Implications of Defining When a Woman Is Pregnant". The Guttmacher Report on Public Policy. May 2005, Volume 8, Number 2. Many of these arguments are related to the anti-abortion movement. In this way of thinking, if the pregnancy has not yet begun, then stopping the process is not abortion and therefore can contain none of the moral issues associated with abortion, but if it is a pregnancy, then stopping it is a morally significant act.

A major complication is that ideological and religious concepts such as "ensoulment" (whether or not a human being is said to have gone from mere matter to having a spiritual entity inside) and "personhood" (whether or not a human being is said to be a distinct individual with innate human rights versus otherwise) exist outside of scientific analysis, and thus many individuals have argued that the beginning of pregnancy cannot be determined strictly through physical evidence alone. No experiment exists (or can exist) to measure the spirituality of an object or living thing in the same way that height, temperature, weight, etc. can be studied.

Some ideological and religious commentaries have argued that pregnancy should be stated as beginning at the first, exact moment of conception in which a human sperm makes full contact with an egg cell. In contrast, other commentaries have argued that the duration of pregnancy begins at some other point, such as when the fertilization process ends (when a new, independent cell genetically distinct from the prior egg and sperm exists) or when implantation occurs (when the new set of cells lodges itself against the uterine wall, allowing it to grow rapidly). The ambiguity's implications mean that, despite the scientific community being able to describe the physical processes in detail, the decision about what should be called "abortion" and what should be called "contraception" or pregnancy prevention are not agreed upon.

Definitions of pregnancy beginning +Comparison of dating systems for a typical pregnancyEventGestational age (from the start of the last menstrual period)Fertilization ageImplantation ageMenstrual period beginsDay 1 of pregnancyNot pregnantNot pregnantHas sex and ovulates2 weeks pregnantNot pregnantNot pregnantFertilization; cleavage stage beginsDay 15Day 1Not pregnantImplantation of blastocyst beginsDay 20Day 6Day 0Implantation finishedDay 26Day 12Day 6 (or Day 0)Embryo stage begins; first missed period4 weeksDay 15Day 9Primitive heart function can be detected5 weeks, 5 daysDay 26Day 20Fetal stage begins10 weeks, 1 day8 weeks, 1 day7 weeks, 2 daysFirst trimester ends13 weeks11 weeks10 weeksSecond trimester ends26 weeks24 weeks23 weeksChildbirth39–40 weeks37–38 weeks36–37 weeks

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."FDA Rejection of Over-The-Counter Status for Emergency Contraception Pills American Medical Association House of Delegates Resolution:443. Retrieved April 30, 2007 Similarly, the British Medical Association has defined an "established pregnancy" as beginning at implantation. "The term 'abortion' is used throughout this paper to refer to the induced termination of an established pregnancy (i.e. after implantation)." The legal definition in the United Kingdom is not clear. – "It is generally assumed that when the Act states that 'pregnancy has not exceeded its 24th week' it means 24 weeks since the first day of the woman's last period. But this is not clear – particularly if there is evidence that conception had taken place on a day after this....The Attorney General said, in 1983 (see Brazier 1992 page 293-4) that there is no pregnancy until implantation. This is persuasive but not binding precedence."

Other definitions exist. The American Heritage Stedman's Medical Dictionary defines "pregnancy" as "from conception until birth."The American Heritage Stedman's Medical Dictionary, 2002 Definitions like this may add to a lay person's confusion, as "conception" in a scientific context may be defined as fertilization, in a medical context can mean either fertilization or implantation but in lay terms may mean both.

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, such as Walter Larimore of the Focus on the Family group, 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.Doctor: Hospital: Medical company: 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.

Although many anti-abortion advocates have argued that both pregnancy and status of a separate human life beginning happen at fertilization, several examples also exist of people within those movements taking alternate views. For example, doctor and social activist Bernard Nathanson wrote in his 1979 work Aborting America that a confirmed moment of implantation should be considered the point at which a distinct human being exists. He specifically stated (note that 'alpha' is his shorthand for an organized group of cells), "Biochemically, this is when alpha announces its presence as part of the human community by means of its hormonal messages, which we now have the technology to receive... know[ing] biochemically that it is an independent organism distinct from the mother."

Legal implications In August 2008, the U.S. Department of Health and Human Services proposed a regulation to protect certain actions of health workers: refusal to provide patient services that the health workers believe to be abortifacient. The ban on discrimination against these employees would apply to all organizations that receive grant money from HHS. A draft version leaked in July proposed that the U.S. federal government define abortion as including "termination of [human] life... before... implantation." The official proposal dropped the definition of abortion, instead leaving it to the objecting individual to define abortion for him- or herself. Groups on both sides of the controversy believe the ban is intended to allow health workers to refuse to dispense IUDs and hormonal contraceptives, including emergency contraception. It has drawn widespread criticism from major medical and health groups.

History In the past, pregnancy has been defined in terms of conception. For example, Webster's Dictionary defined "pregnant" (or "pregnancy") as "having conceived" (or "the state of a female who has conceived"), in its 1828 and 1913 editions.Webster’s Revised Unabridged Dictionary (1913 and 1828) via the ARTFL Project. See definitions of "pregnant" and "pregnancy". However, in the absence of an accurate understanding of human development, early notions about the timing and process of conception were often vague.

Both the 1828 and 1913 editions of Webster's Dictionary said that to "conceive" meant "to receive into the womb and ... begin the formation of the embryo." However most references say that it was only in 1875 that Oskar Hertwig discovered that fertilization includes the penetration of a spermatozoon into an ovum. Thus, the term "conception" was in use long before the details of fertilization were discovered. By 1966, a more precise meaning of the word "conception" could be found in common-use dictionaries: the formation of a viable zygote.Webster’s Third New International Dictionary (1966), defining conception as the "act of becoming pregnant (formation of a viable zygote); state of being conceived; that which is conceived (embryo, fetus)..." quoted in Mallett Shelley, Conceiving Cultures , p. 284 (U. Mich. 2003).

In 1959, Dr. Bent Boving suggested that the word "conception" should be associated with the process of implantation instead of fertilization.Boving, B.G., "Implantation Mechanisms", in Mechanics Concerned With Conception. Hartman, C.G., ed. (Pergamon Press 1963), page 386. Some thought was given to possible societal consequences, as evidenced by Boving's statement that "the social advantage of being considered to prevent conception rather than to destroy an established pregnancy could depend on something so simple as a prudent habit of speech." In 1965, the American College of Obstetricians and Gynecologists (ACOG) adopted Boving's definition: "conception is the implantation of a fertilized ovum."American College of Obstetricians and Gynecologists Terminology Bulletin. Terms Used in Reference to the Fetus. No. 1. Philadelphia: Davis, September, 1965.

The 1965 ACOG definition was imprecise because, by the time it implants, the embryo is called a blastocyst,Biggers, J., "Ambiguity of the Word Conception: Implications if S. 158 is Enacted", The Human Life Bill Appendix, Hearings Before the Subcommittee on Separation of Powers of the Committee on the Judiciary, United States Senate, p. 281-288 (1982). so it was clarified in 1972 to "Conception is the implantation of the blastocyst."Hughes, E.C. "Gametogenesis and Fertilization", in Obstretric-Gynecologic Terminology. Philadelphia: Davis, 1972: 299–304. Some dictionaries continue to use the definition of conception as the formation of a viable zygote.Dictionary.com.

Birth control – mechanism of action

Birth control methods usually prevent fertilization. This cannot be seen as abortifacient because, by any of the above definitions, pregnancy has not started. However, emergency contraception might have a secondary effect of preventing implantation, thus allowing the embryo to die. Those who define pregnancy from fertilization subsequently may conclude that the agents should be considered abortifacients.

Speculation about post-fertilization mechanisms is widespread, even appearing on patient information inserts for hormonal contraception, but there is no clinical support. One small study, using fourteen women, might be considered as providing evidence of such an effect for IUDs, which cites: and a study of the combined oral contraceptive pill has been proposed.

Possibly affected methods