Abortion, termination of pregnancy before the foetus is capable of independent life. When the expulsion from the uterus occurs after the foetus becomes viable (capable of independent life), usually at the end of six months of pregnancy, it is technically a premature birth. In the United Kingdom, when the foetus is not born alive after 24 weeks of pregnancy it is termed a still birth.
II. Types of AbortionPrint section
Abortion may be spontaneous or induced. Expelled foetuses weighing less than 0.5 kg (18 oz) or of less than 20 weeks' gestation are usually considered abortions.
A. Spontaneous AbortionPrint section
It is estimated that some 25 per cent 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 have also been found in women who are subject to recurrent abortions. Spontaneous abortions may also be caused by such maternal abnormalities as acute infectious diseases, systemic diseases such as nephritis and diabetes, and severe trauma. Uterine malformations, including tumours, are responsible in some instances.
The most common symptom of threatened abortion is vaginal bleeding, with or without intermittent pain. About a quarter of all pregnant women bleed at some time during early pregnancy, however, and up to 50 per cent of these women carry the foetus to 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 may also 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 doctors advocate the surgical removal of any residual embryonic or placental tissue in order to avoid possible irritation or infection of the uterine lining.
B. Induced AbortionPrint section
Induced abortion is the deliberate termination of pregnancy by removal of the foetus from the uterus. 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...