Contragestion
Encyclopedia
Blastocyst
The blastocyst is a structure formed in the early embryogenesis of mammals, after the formation of the morula. It is a specifically mammalian example of a blastula. It possesses an inner cell mass , or embryoblast, which subsequently forms the embryo, and an outer layer of cells, or trophoblast,...
, or a device or substance which can effect such prevention as a means of birth control
Birth control
Birth control is an umbrella term for several techniques and methods used to prevent fertilization or to interrupt pregnancy at various stages. Birth control techniques and methods include contraception , contragestion and abortion...
. Other birth control
Birth control
Birth control is an umbrella term for several techniques and methods used to prevent fertilization or to interrupt pregnancy at various stages. Birth control techniques and methods include contraception , contragestion and abortion...
methods include contraception
Contraception
Contraception is the prevention of the fusion of gametes during or after sexual activity. The term contraception is a contraction of contra, which means against, and the word conception, meaning fertilization...
, which prevents fertilization, and abortion
Abortion
Abortion is defined as the termination of pregnancy by the removal or expulsion from the uterus of a fetus or embryo prior to viability. An abortion can occur spontaneously, in which case it is usually called a miscarriage, or it can be purposely induced...
, the removal or expulsion of a fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
or embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
from the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
). Contragestives include intrauterine devices placed inside the uterus and some forms of hormonal "emergency contraception
Emergency contraception
Emergency contraception , or emergency postcoital contraception, refers to birth control measures that, if taken after sexual intercourse, may prevent pregnancy.Forms of EC include:...
".
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 BaulieuÉtienne-Émile Baulieu
Étienne-Émile Baulieu is a French biochemist and endocrinologist who is best known for his research in the field of steroid hormones and their role in reproduction and aging.-Biography:...
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 implantationImplantation
In humans, implantation is the beginning of pregnancy, in which the embryo Adheres to the wall of the uterus. At this stage of prenatal development, the embryo is a blastocyst...
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
- 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 abortifacientAbortifacientAn abortifacient is a substance that induces abortion. Abortifacients for animals that have mated undesirably are known as mismating shots....
terminates the pregnancy before the fetus achieves viability.
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
Mifepristone
Mifepristone is a synthetic steroid compound used as a pharmaceutical. It is a progesterone receptor antagonist used as an abortifacient in the first months of pregnancy, and in smaller doses as an emergency contraceptive. During early trials, it was known as RU-38486 or simply RU-486, its...
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.
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 catsand studies indicate that insufficient calcitonin causes contragestion in rats.
Rodents also display something called the Bruce effect
Bruce effect
The Bruce effect, or pregnancy block, refers to the tendency for female rodents to terminate their pregnancies following exposure to the scent of an unfamiliar male. The effect has primarily been studied in laboratory mice , but is also observed in deer-mice, meadow voles, and collared lemmings...
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.See also
- Birth ControlBirth controlBirth control is an umbrella term for several techniques and methods used to prevent fertilization or to interrupt pregnancy at various stages. Birth control techniques and methods include contraception , contragestion and abortion...
- Beginning of pregnancy controversyBeginning of pregnancy controversyControversy 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...
- Reproductive technologyReproductive technologyReproductive technology encompasses all current and anticipated uses of technology in human and animal reproduction, including assisted reproductive technology, contraception and others.-Assisted reproductive technology:...