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Controversy over the beginning of pregnancy usually occurs in the context of the abortion debate. Different definitions are used to define certain birth control methods as either contraceptives or abortifacients, because of their possible post-fertilisation effects.
Definitions of pregnancy beginning
Traditionally, doctors have measured pregnancy from a number of convenient points, including the day of last menstruation, ovulation, fertilisation, 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.
The definition of pregnancy as starting from implantation has been adopted by the American Medical Association. Likewise, the British Medical Association defines pregnancy from implantation, and this is the legal definition in the United Kingdom. - See the section 'Inter-uterine contraceptive devices (IUCDs) and "morning after" pills'
Despite this, other definitions are frequently used. The American Heritage® Stedman's Medical Dictionary defines "pregnancy" as "from conception until birth." The American Heritage® Stedman's Medical Dictionary, 2002 Prominent medical textbooks such as Langman's Medical Embryology count pregnancy from fertilisation,O'Brian, Patrick and Thomas Sadler. Langman's Medical Embryology. Lippincott Williams & Wilkins (2004), p. 117. Professionals have also debated the issue in medical journals. Larimore, Walter L., MD, et al. "Response: Does Pregnancy Begin at Fertilization?" Family Medicine, November-December 2004.
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. However in this system, ovulation and fertilisation do not occur until 2 out of the 40 weeks counted have passed.
Types of contraception
Birth control methods usually prevent either fertilisation or implantation. Those that prevent fertilisation cannot be seen as abortifacient because, by any of the above definitions, pregnancy has not started. However, those that prevent implantation can be seen as abortifacient by those that classify the start of pregnancy as fertilisation.
Affected birth control methods
- Hormonal contraception works primarily by preventing ovulation, but may have a secondary effect of interfering with implantation of embryos.
- Intrauterine devices work primarily by spermicidal/ovicidal effects, but may have a secondary effect of interfering with the development of pre-implanted embryos.
- The Lactational Amenorrhea Method works primarily by preventing ovulation, but is also known to cause luteal phase defect (LPD). LPD is believed to interfere with the implantation of embryos Diaz, S. et. al. Relative contributions of anovulation and luteal phase defect to the reduced pregnancy rate of breastfeeding women. Fertility and Sterility. 1992 Sep;58(3):498-503. PMID 1521642..
- Fertility awareness methods work primarily by preventing conception, but it has been suggested they have a secondary effect of creating embryos incapable of implanting (due to aged gametes at the time of fertilisation).
Ethics of preventing pregnancy
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. The use of hormonal contraceptives, including emergency contraception, is usually motivated by an intention to avoid pregnancy. However, it can also be a side effect of a treatment for various medical conditions. Also, breastfeeding greatly suppresses ovulation, but occasionally some ova may be released – luteal phase defect, caused by breastfeeding, makes the uterine lining hostile to implantation and as such prevents implantation after fertilisation. 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. However, when implantation prevention is unintentionally caused as a side effect such pro-life groups do not consider the practice to be immoral, citing the bioethical principle of double effect Doesn't breastfeeding do the same thing as the Pill? Eternal Perspective Ministries, 2006. Accessed May 2006..
In vitro fertilisation and detectable pregnancy
The advent of in vitro fertilisation allowed fertilisation to occur in a Petri dish instead of inside a woman. This clearly made fertilisation an event that did not automatically result in pregnancy.
All 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 tested for.
Viability and established pregnancy
A related issue that comes up in this debate is how often fertilisation leads to an established, viable pregnancy. Current research suggests that fertilised embryos naturally fail to implant some 30% to 60% of the time.Kennedy, T.G. Physiology of implantation. 10th World Congress on in vitro fertilisation and assisted reproduction. Vancouver, Canada, 24-28 May 1997. Of those that do implant, about 25% are miscarried in the first two weeks after pregnancy can be detected.Wilcox AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus and loss of pregnancy. New England Journal of Medicine. 1999;340(23):1796-1799. PMID 10362823. As a result, the majority of zygotes never result in established pregnancies, much less birth.
References
"Beginning of pregnancy controversy"