Kategorie: Biológia (celkem: 966 referátů a seminárek)

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  • Přidal/a: anonymous
  • Datum přidání: 05. července 2007
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Abortion, termination of pregnancy before the fetus is capable of independent life. When the expulsion from the womb occurs after the fetus becomes viable (capable of independent life), usually at the end of six months of pregnancy, it is technically a premature birth.

Types of Abortions
Abortion may be spontaneous or induced. Expelled fetuses weighing less than 0.50 kg or of less than 20 weeks' gestation are usually considered abortions.

It is estimated that some 25 percent of all human pregnancies terminate spontaneously in abortion, with three out of four abortions occurring during the first three months of pregnancy. Some women apparently have a tendency to abort, and recurrent abortion decreases the probability of subsequent successful childbirth.
The causes of spontaneous abortions, or miscarriages, are not clearly established. Abnormal development of the embryo or placental tissue, or both, is found in about half the cases; these abnormalities may be due to inherent faults in the germ cells or may be secondary to faulty implantation of the developing ovum or to other characteristics of the maternal environment. Severe vitamin deficiencies have been shown to play a role in abortions in experimental animals. Hormone deficiencies also have been found in women who are subject to recurrent abortions. Spontaneous abortions may be caused also by such maternal abnormalities as acute infectious diseases, systemic diseases such as nephritis and diabetes, and severe trauma. Uterine malformations, including tumors, are responsible in some instances, and extreme anxiety and other psychic disturbances may contribute to the premature expulsion of the fetus. The most common symptom of threatened abortion is vaginal bleeding, with or without intermittent pain. About one-fourth of all pregnant women bleed at some time during early pregnancy, however, and up to 50 percent of these women carry the fetus for the full term. Treatment for threatened abortion usually consists of bed rest. Almost continuous bed rest throughout pregnancy is required in some cases of repeated abortion; vitamin and hormone therapy also may be given. Surgical correction of uterine abnormalities may be indicated in certain of these cases.
Spontaneous abortion may result in expulsion of all or part of the contents of the uterus, or the embryo may die and be retained in the uterus for weeks or months in a so-called missed abortion.

Most physicians advocate the surgical removal of any residual embryonic or placental tissue in order to avoid possible irritation or infection of the uterine lining.

Induced abortion is the deliberate termination of pregnancy by removal of the fetus from the womb. It is currently performed by any of four standard procedures, according to the period of gestation. Suction, or vacuum aspiration, is used in the first trimester (up to 12 weeks). In this procedure, which normally takes five to ten minutes on an outpatient basis, the cervix (neck of the uterus) is opened gradually with a series of dilators and the uterine contents are withdrawn by means of a small flexible tube called a cannula, which is connected to a vacuum pump. To ensure that no fragments of tissue remain, a spoon-tipped metal instrument called a curette may then be used to scrape the uterine lining. Introduced in China in 1958, vacuum aspiration soon replaced the traditional early-abortion procedure, dilation and curettage (D&C), in which the curette is used to dislodge the fetus. Pregnancies in the earlier part of the second trimester may be terminated by a special suction curettage, sometimes combined with forceps, in a procedure called dilation and evacuation (D&E). The patient may remain in the hospital overnight and may experience a menstrual type of bleeding and discomfort. After the 15th week of gestation, saline infusion is commonly used. In this technique, a small amount of amniotic fluid is withdrawn from the uterus by means of a fine tube or hypodermic needle through the abdominal wall and is slowly replaced with a strong (about 20 percent) salt solution. This induces uterine contractions in about 24 to 48 hours. The fetus is then usually quickly expelled and the patient leaves the hospital about a day later. Late abortions are accomplished by hysterotomy; this is a major surgical procedure, similar to a cesarean section but requiring a much smaller incision lower in the abdomen. An alternative to these procedures is RU-486, a pill that blocks the hormone progesterone and is effective in the first 50 days of gestation. RU-486 was developed in France and approved for sale there in 1988. As of early 1993 it remained untested in the United States.
When performed under proper clinical conditions, first-trimester abortions are relatively simple and safe. The likelihood of complications increases with length of gestation and includes infection, cervical injury, perforation of the uterus and hemorrhage. Recent data, however, show that even late abortions place the patient at less risk than full-term delivery.

Regulation of Abortion
The practice of abortion was widespread in ancient times as a method of birth control.

Later it was restricted or forbidden by most world religions, but it was not considered an offense in secular law until the 19th century. During that century, first the English Parliament and then American state legislatures prohibited induced abortion to protect women from surgical procedures that were at the time unsafe, commonly stipulating a threat to the woman's life as the sole (“therapeutic”) exception to the prohibition. Occasionally the exception was enlarged to include danger to the mother's health as well.
Legislative action in the 20th century has been aimed at permitting the termination of unwanted pregnancies for medical, social, or private reasons. Abortions at the woman's request were first allowed in post-revolutionary Russia in 1920, followed by Japan and several East European nations after World War II (1939-1945). In the late 1960s liberalized abortion regulations became widespread. The impetus for the change was threefold: (1) infanticide and the high maternal death rate associated with illegal abortions, (2) a rapidly expanding world population, (3) the growing feminist movement. By 1980, countries where abortions were permitted only to save a woman's life contained about 20 percent of the world's population. Countries with moderately restrictive laws—abortions permitted to protect a woman's health, to end pregnancies resulting from rape or incest, to avoid genetic or congenital defects, or in response to social problems such as unmarried status or inadequate income—contained some 40 percent of the world's population. Abortions at the woman's request, usually with limits based on physical conditions such as duration of pregnancy, were allowed in countries with nearly 40 percent of the world's population.

U.S. Legislation
In the United States, legislation followed the world trend. The moderately restrictive type of abortion law was adopted by 14 states between 1967 and 1972. Alaska, Hawaii, New York, and Washington legislated abortion on request with few restrictions. In 1973 the Supreme Court of the United States, in the case of Roe v. Wade, declared unconstitutional all but the least restrictive state statutes. Noting that induced early abortions had become safer than childbirth and holding that the word person in the Constitution of the United States “does not include the unborn,” the Court defined, within each of the three stages of pregnancy, the reciprocal limits of state power and individual freedom:
“(a) During the first trimester, the abortion decision and its effectuation must be left to the medical judgment of the pregnant woman's attending physician.

(b) After the first trimester, the State, in promoting its interest in the health of the mother, may, if it chooses, regulate the abortion procedure in ways that are reasonably related to maternal health. (c) For the stage subsequent to viability, the State, in promoting its interest in the potentiality of human life may, if it chooses, regulate and even proscribe abortion, except where it is necessary, in appropriate medical judgment, for the preservation of the life or health of the mother.”

Resistance and Controversy
Opponents of the 1973 Supreme Court ruling, arguing that a fetus is entitled as a “person” to constitutional protection, attacked the decision on a variety of fronts. State legislative bodies were lobbied for statutes narrowing the implications of the decision and circumscribing in several ways the mother's ability to obtain an abortion. A nationwide campaign was instituted to amend the Constitution to prohibit or severely restrict abortion. “Right-to-life” groups also engaged in grass-roots political activity designed to defeat abortion proponents and elect abortion opponents. Abortion became, rather than simply a legal and constitutional issue, a major political and social controversy. Many state legislatures passed laws imposing additional procedural requirements on women who sought abortions; federal court decisions holding these new statutes unconstitutional usually followed each legislative initiative.

Recent Developments
The Reagan administration (1981-1989) and the Bush administration (1989-1992) supported the right-to-life position, as did many of their appointees to the federal judiciary. The Supreme Court, though sharply divided, generally declared unconstitutional those laws it found to place an undue burden on a woman's right to obtain an abortion. For example, in 1983 the Court reviewed three laws—from Akron, Ohio; Missouri; and Virginia—and struck down provisions requiring (1) a 24-hour waiting period; (2) that a doctor obtain a woman's “informed consent”; and (3) hospitalization for abortions after the first trimester of pregnancy. At the same time the Court upheld a Missouri provision that required a minor to obtain parental consent before an abortion but struck down an Akron ordinance with the same objective but which a majority of the justices found unduly restrictive. In a 1989 decision the Court let stand a Missouri requirement that before performing an abortion on any woman thought to be at least 20 weeks pregnant, a doctor must test whether the fetus could survive outside the womb.

In a wide-ranging decision in 1992 on a Pennsylvania law, the Court reiterated its general support for a woman's right to an abortion but upheld most provisions of the statute, including requirements for “informed consent,” a mandatory waiting period, and the consent of at least one parent or a judge for anyone age 16 or younger. In 1991 the Court had upheld a Reagan administration executive order banning abortion counseling at federally funded clinics. Fulfilling a campaign promise, President Bill Clinton reversed this ban in January 1993.
During the 1970s and 1980s legislative action was often effective in cutting off public funds for abortions. In 1977 the Supreme Court ruled that neither the Social Security Act nor the Constitution prevented a state from restricting the use of Medicaid funds for “medically necessary” abortions. In a companion case, the Court held that a city may refuse to allow elective abortions to be performed in a municipal hospital. Subsequently, a congressional limitation of Medicaid eligibility for elective abortions (the Hyde Amendment) was upheld. In 1989 the Court upheld a Missouri statute barring all public employees and taxpayer-supported facilities from performing abortions unless the pregnant woman's life is at stake.

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