Infant mortality is a concept in demography that estimates the "rate of deaths occurring in the first year of life". (reference for quote: Medline-Plus Medical dictionary (an on line service of the U.S. National Library of Medicine and the National Institutes of Health). That rate is calculated by taking the number of infants who perish in a given population over a period of time, as compared to the total number of all infants in the population. Since death in infancy is never normal, death rates of infants are used as evidence of detrimental conditions. Infant mortality is the major factor in lowering life expectancy.
When infant mortality is looked at in a particular population, that population is chosen in order to examine some question or thesis. For example, which conditions are most important in determining the health of infants? One way to measure the importance of different illnesses or medical diagnoses in infants is to calculate the infant mortality that is attributed to each. If infants with a particular diagnosis have a high death rate, that alone is reason to be concerned about such a medical condition in terms of health care.
At present, in stable developed countries, infant mortality is primarily due to: prematurity, birth defects, sudden infant death syndrome, and accidents. In less developed countries without modern health care, infectious causes such as neonatal tetatnus and both bacterial and viral gastrointestinal infections are major causes of infant mortality. In areas of war, natural disaster and extreme poverty, starvation is an underlying cause of infant mortality, making babies less able to recover from infectious diseases or other ailments.
Infant mortality is also an important measure in demographics, and is often referred to by historians, politicians, and civic planners, who use this number as an indicator for the socioeconomic status of a given society.
With technological advances in invitro fertilization and health care, the correlation between wealth, access to health care, and high infant survival rates are not straight-forward for all populations. For example, prematurity and low birth weights are common in multiple births, and these are more common in assisted reproduction. Prematurity and low birth weights are also more common in babies born to mothers who have poor nutrition (starvation) during pregnancy, and to those who smoke tobacco, engage in substance abuse, and neglect to have prenatal care. Selected populations at socioeconomic extremes, then, can be more likely to have a high infant mortality.
Babies are at high risk when human populations face starvation or the unsanitary conditions produced by overcrowding and poverty, or both. There is an association between poverty and high infant mortality.
Infant mortality in pediatrics
Unintentional injury and homicide
In the United States, during the years 1999--2002, the injury death rate among infants was 33.7/100,000 population."The three leading mechanisms of unintentional injury death among infants aged <1 year, regardless of race or ethnicity, were suffocation, motor-vehicle (MV)--traffic injury, and drowning.
Infant mortality in demographic history
The remarkable declines in Australian infant mortality rates from 1870 to 1950 were part of the famous demographic transition that was shared by European and English-speaking countries. Mothers and babies movements claimed, and have often been given, credit for much of this improvement, at least since 1900. Smith has examined mothers' practices, especially whether or not the advice presented to mothers resulted in desirable changes in behavior and thereby reduced the infant death rate. Prescription and practice exhibited different chronologies of change. Until 1930 in Australia, the proportion of breastfed babies remained fairly stable at a high level; from the 1930s, breastfeeding declined despite the expansion of the local infant welfare movement. Historians cannot judge the relative effectiveness of alleged main contributors to the infant mortality decline without considering mothers' behavior. "Mothering," however enjoined, varied in its effectiveness by class. Mothers often rationally, or by necessity, ignored the experts.
- P. Congdon, R. M. Campos, S. E. Curtis, H. R. Southall, I. N. Gregory, I. R. Jones, "Quantifying and explaining changes in geographical inequality of infant mortality in England and Wales since the 1890s," International Journal of Population Geography Volume 7, Issue 1, Date: January/February 2001, Pages: 35-51
- Shi Wu Wen, Shiliang Liu, K.S. Joseph, Jocelyn Rouleau, Alexander Allen. "Patterns of infant mortality caused by major congenital anomalies," Teratology Volume 61, Issue 5, Date: May 2000, Pages: 342-346
- Greg R. Alexander, Martha Slay. "Prematurity at birth: Trends, racial disparities, and epidemiology," Mental Retardation and Developmental Disabilities Research Reviews Volume 8, Issue 4, Date: 2002, Pages: 215-220
- Meckel, Richard A. Save the Babies: American Public Health Reform and the Prevention of Infant Mortality, 1850-1929. Johns Hopkins U. Press, 1990. 302 pp.
- Stephanie J. Bernard, PhD, Leonard J. Paulozzi, MD L.J. David Wallace, MSEH (Division of Unintentional Injury Prevention, National Center for Injury Prevention and Control) Fatal Injuries Among Children by Race and Ethnicity --- United States, 1999--2002. MMWR May 18, 2007 / Vol. 56 / No. SS--5 
- Philippa Mein Smith, "Mothers, Babies, and the Mothers and Babies Movement: Australia Through Depression and War." Social History of Medicine 1993 6(1): 51-83. Issn: 0951-631x