Controversy over the 'beginning of pregnancy' usually occurs in the context of the abortion debate. Depending on where pregnancy is considered to begin, some methods of birth control or infertility treatment might be considered abortifacient. The controversy is not a scientific issue since knowledge of human reproduction and development has become very refined. Rather, the issue has social, political and legal ramifications since some equate the 'beginning of pregnancy' with the 'beginning of [individual's] life'. The latter question may have no clear definition since, biologically, life is usually regarded as a continuum.
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 considered a controversial 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." The resolution passed by a majority vote, despite the opposition of the American Academy of Family Physicians.
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." There has been some debate on the matter of definition in medical journals.
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.
Previously, pregnancy was defined in terms of conception. However, in the absence of an accurate understanding of human development, early notions about the timing and process of conception were often vague. For example, ''Webster's Dictionary'' defines "pregnant" (or "pregnancy") as "having conceived" (or "the state of a female who has conceived"), in its 1828 and 1913 editions.
Both the 1828 and 1913 editions of ''Webster's Dictionary'' said that to "conceive" meant "to begin the formation of the embryo." 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.
In 1959, Dr. Bent Boving suggested that the word "conception" should be associated with the process of implantation instead of fertilization. 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."
The 1965 ACOG definition was imprecise because, by the time it implants, the zygote is called a blastocyst, so it was clarified in 1972 to "Conception is the implantation of the blastocyst." Some dictionaries continue to use the definition of conception as the formation of a viable zygote.
Birth control methods usually prevent fertilization. This cannot be seen as abortifacient because, by any of the above definitions, pregnancy has not started. However, some methods might have a back-up effect of preventing implantation, thus allowing the zygote to die. Those who define pregnancy from fertilization subsequently 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. and a study of the combined oral contraceptive pill has been proposed.
The advent of in vitro fertilisation allowed fertilisation to occur in a Petri dish instead of inside a woman. This clearly made fertilization an event that did not automatically result in pregnancy.
A related issue that comes up in this debate is how often fertilization leads to an established, viable pregnancy. Current research suggests that fertilized embryos naturally fail to implant some 30% to 60% of the time.Kennedy, T.G. Physiology of implantation. 10th World Congress on in vitro fertilization and assisted reproduction. Vancouver, Canada, 24-28 May 1997. Of those that do implant, about 25% are miscarried by the sixth week LMP (after the woman's Last Menstrual Period). As a result, even without the use of birth control, between 48% and 70% of zygotes never result in established pregnancies, much less birth.
The intention of a woman to prevent pregnancy is an important factor in whether or not the act of contraception is seen as abortive by some pro-life groups. Hormonal contraceptives have a possible effect of preventing implantation of a blastocyst, as discussed previously. Use of these drugs with the intention of preventing pregnancy is seen by some pro-life groups as immoral. This is because of the possibility of causing what they believe to be an abortion.
However, hormonal contraception can also be used as a treatment for various medical conditions. When implantation prevention is unintentionally caused as a side effect of medical treatment, such pro-life groups do not consider the practice to be immoral, citing the bioethical principle of double effect. Likewise, when a hormonal contraceptive is used with the intention of preventing fertilisation, the intended reduction in implantation failures, miscarriages and deaths from childbearing may outweigh the possibility that the method might cause some implantation failures.
A related application of the principle of double effect is breastfeeding. Breastfeeding greatly suppresses ovulation, but eventually an ovum is released. Luteal phase defect, caused by breastfeeding, makes the uterine lining hostile to implantation and as such may prevent implantation after fertilization. Some pro-choice groups have expressed concern that the movement to recognize hormonal contraceptives as abortifacient will also cause breastfeeding to be considered an abortion method.
A protein called early pregnancy factor (EPF) is detectable in a woman's blood within 48 hours of ovulation if fertilization has occurred. However, testing for EPF is time consuming and expensive; most early pregnancy tests detect human chorionic gonadotropin (hCG), a hormone that is not secreted until after implantation. Defining pregnancy as beginning at implantation thus makes pregnancy a condition that can be easily tested for.
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