User:OckRaz/sandbox

Contragestion is the prevention of implantation of the blastocyst, or a device or substance which can effect such prevention as a means of birth control. Other birth control methods include contraception, which prevents fertilization, and abortion, the removal or expulsion of a fetus or embryo from the uterus. Contragestives may include intrauterine devices placed inside the uterus and some forms of hormonal "emergency contraception".

Terminology
The term, 'contraception' is a contraction of 'contra', which means 'against', and the word 'conception', which is a non-technical term that is synonymous with fertilization. The word 'contragestion' is likewise a combination of 'contra' and 'gestation'. French scientist Étienne-Émile Baulieu coined the word in 1985 because he felt that there was a need for a technical term to describe the prevention of implantation, which did not fit the traditional definitions of either 'contraception' or 'abortion'. Elisabeth Johannisson of the International Committee for Research in Reproduction endorsed the use of this nomenclature saying that, "it is appropriately descriptive and fits in with contemporary medical ethics, which require us to indicate (when we know them) the phenomena which occur in patients. The word 'contraception' is ambiguous and 'abortion' remains the traumatic symbol of a painful failure... Faced with the imprecision of these currently used terms, 'contragestion' is preferable because it takes recent scientific knowledge into account.  At the same time, it is difficult to make this term accepted because more classical expressions have great force.  The word 'abortion' has a long tradition... The word 'contraception' has had a strong impact on the history of our century.  Between the two it is difficult to find a place, either biological or semantic." It is also worth noting that since 18 U.S. states define pregnancy as beginning at conception, describing methods of birth control in terms of their potential means of action allows one to be technically accurate while using language that is neutral with regard to the abortifacient versus contraceptive controversy.

Contragestion and birth control
The function of birth control can be classified by the stage of reproduction during which it is active. A form of birth control which prevents the sperm from fertilizing the egg is a contraceptive agent. A form of birth control which acts after fertilization to prevent or interrupt the implantation of the embryo into the uterine lining is a contragestive agent. After implantation has occurred, an agent which ends gestation by terminating the pregnancy is an abortifacient It is important to bear in mind that these mechanisms of action are not mutually exclusive. One substance or device can have more than one potential effect depending upon when it is used. For example, while mifepristone is best known as an abortifacient, it can also function as a contragestive agent. Likewise, the IUD can be used as a contraceptive or a contragestive depending upon when it is inserted.
 * ''Contraception occurs when an agent prevent the sperm from fertilizing the egg
 * ''Contragestion occurs when an agent prevents or interrupts implantation of the embryo or causes the uterine lining to shed during the implantation period
 * ''An abortion has taken place if, after implantation has occurred, an abortifacient terminates the pregnancy before the fetus achieves viability.

Naturally occurring contragestion
Implantation is a delicate and complicated process which can be affected by a variety of factors. The result is that contragestion occurs naturally in both humans and other animals for many reasons.

In animals
One factor which can cause contragestion is malnutrition. For example, a deficiency of vitamin A can cause contragestion in cats and studies indicate that insufficient calcitonin causes contragestion in rats. Rodents also display something called the Bruce effect wherein exposure to the scent of an unfamiliar male causes contragestion. Environmental factors are also a cause of contragestion. Toxins can cause contragestion in both animals and humans, with exposure to dioxins preventing 70% of implantation of mouse embryos.

In humans
Contragestion is a relatively common occurrence in humans. Estimates of the rate of contragestion within the human population as a whole vary greatly, from as low as 30% to as high as 70%, with actual testing of healthy women attempting conception revealing a rate of 36%. Many embryos  are incapable of implantation because they are not properly formed. According to Lynn Wiley, professor of obstetrics and gynecology, "Only certain cells within the embryo can implant and form a placenta. Without these cells, or if these cells are not healthy, implantation will fail." Features of the uterine environment can also cause contragestion. These features include, but are not limited to anatomic abnormalities, hormonal irregularities, and malfunctions in the immune system.