Abortion is any interruption of pregnancy before 28 weeks of gestation, resulting in a dead foetus. Death of the foetus thereafter is called foetal death. Spontaneous human abortion may take the form of foetal infection and death, or uterine contraction and rejection of the partially formed foetus which may be malformed or have congenital anomalies. Spontaneous abortion may be habitual. It may occur as a result of disease, malnutrition, genetic defects including radiation, ageing, multiple pregnancies or emotional disorder. Women who smoke during pregnancy have a 27% higher chance of miscarriage. If resulting from disease this may be that of the prospective mother or father. Spontaneous abortion may result in death or the continuance of disease complications or emotional disorder. It may create marital and family problems resulting in breakdown. Although miscarriage may be more common than childbirth, women are not prepared for the possibility or for the callousness with which their feelings of loss and bereavement are dismissed by relatives and medical practitioners.
The incidence of spontaneous abortion cannot be estimated accurately because of: the unrepresentative nature of populations available for study in the world; understatement due to failure to recognize abortion, lack of recall and lack of rapport between the woman and the interrogator; over statement, misreporting of temporary amenorrhoea, etc. A reasonable estimate seems to be an over-all-ratio of 15-20 spontaneous abortions per 100 pregnancies (WHO report, 1970). Because of the high percentage of genetic aberrations, between 12 and 15% of of all embryos die within a few days or weeks, without the mother being especially aware of it. Between the second and sixth month about 10 to 15% more will die as spontaneous miscarriages. According to a 1992 British report, an estimated 4,300 miscarriages per year are the result of maternal tobacco smoking.
In Australia in 2000, it was estimated that there was one abortion every 2 minutes.