Infant mortality is the death of a child before reaching one year of age, and the infant mortality rate is the standard demographic measure used to describe the frequency of such deaths. It is commonly expressed as the number of deaths among infants under one year of age per 1,000 live births in a specified population and period. The denominator is live births rather than the total population because infant mortality concerns the survival of newborn children.
The measure is distinct from the under five mortality rate, which includes children dying at any time before their fifth birthday, and from neonatal mortality, which concerns deaths during the first 28 completed days of life. Infant mortality is an important indicator of population health because infant survival is influenced by maternal health, pregnancy care, birth conditions, newborn care, nutrition, infection, sanitation, socioeconomic circumstances and access to medical services.
Infant mortality is commonly divided into neonatal and postneonatal mortality. Neonatal mortality refers to deaths during the first 28 days of life, while postneonatal mortality refers broadly to deaths from 28 days through the first year of life. Neonatal deaths are often strongly associated with prematurity, congenital conditions, complications during pregnancy and childbirth, birth asphyxia, infections and inadequate newborn care.
Postneonatal deaths are more strongly influenced in many settings by infectious diseases, malnutrition, injuries, environmental conditions and household circumstances, although the exact causes vary substantially by population. This distinction is useful because a country can reduce postneonatal mortality while continuing to face significant neonatal mortality, requiring different health interventions. Infant mortality is therefore not a single disease outcome but a summary measure reflecting multiple biological, medical, environmental and social processes.
Historically, infant mortality was much higher in many populations because infectious diseases, malnutrition, poor sanitation, limited obstetric care and inadequate newborn treatment caused large numbers of deaths. Major reductions occurred as clean water supplies, sanitation systems, vaccination, antibiotics, improved nutrition, safer childbirth, breastfeeding support, neonatal medicine and wider healthcare access developed. Public health interventions have therefore played a major role alongside advances in clinical medicine.
The decline in infant mortality has also contributed substantially to increases in life expectancy because deaths during the first year of life have a large effect on the average number of years lived from birth. Falling infant mortality is consequently one of the important demographic changes associated with the demographic transition from high mortality and high fertility towards lower mortality and lower fertility.
Infant mortality is closely connected with maternal and perinatal health. A mother's health before and during pregnancy can influence fetal development, birthweight, gestational age and the risk of complications. Access to antenatal care can help identify and manage conditions that threaten pregnancy, while skilled attendance at birth and appropriate emergency obstetric services can reduce deaths associated with complications. After birth, newborn temperature management, feeding support, infection prevention and treatment, respiratory support and early recognition of illness can affect survival. These relationships demonstrate why infant mortality cannot be interpreted solely as a measure of paediatric healthcare. It reflects the entire chain of conditions surrounding pregnancy, childbirth and early infancy, including social determinants such as poverty, housing, education, nutrition and access to services.
Infant mortality is also an important measure of inequality. National averages can conceal substantial differences between regions, income groups and other population groups. Infants born in disadvantaged circumstances may experience higher exposure to inadequate nutrition, unsafe housing, pollution, infectious disease, limited healthcare access and other risks. Comparisons between countries must also account for differences in registration practices, definitions, medical certification and statistical estimation.
Extremely premature infants, for example, may be classified differently under different registration systems, which can affect reported mortality rates. International organisations therefore use standard definitions and adjustment methods when producing comparable statistics. The numerical rate should always be interpreted alongside information about how births and infant deaths are registered and measured.
Infant mortality differs from stillbirth. A stillbirth refers to a fetal death occurring before or during delivery according to the applicable gestational and registration definition, whereas an infant death occurs after a live birth. The distinction matters statistically because live births enter the denominator of the infant mortality rate. Infant mortality also differs from maternal mortality, which concerns deaths of women associated with pregnancy and its management. Another distinction is between infant mortality and child mortality more broadly. Infant mortality focuses on the first year of life, a period in which biological vulnerability is particularly high, while under five mortality captures a wider childhood period. These measures are related but provide different information about survival and health conditions.
Infant mortality can influence population structure and demographic development in several ways. When infant and child mortality fall, parents may perceive a greater probability that their children will survive to adulthood, which historically has been associated in many populations with eventual reductions in desired family size and fertility. Lower infant mortality also increases the number of children surviving into later life, affecting future age structures.
In demographic analysis, declining infant mortality is therefore both a health outcome and an important component of broader population change. However, fertility decisions are influenced by many factors, including education, economic conditions, contraception, social norms, family preferences and gender relations, so falling infant mortality should not be treated as a single direct cause of fertility decline in every setting.
The infant mortality rate is especially valuable because it provides a relatively sensitive indicator of the conditions affecting the earliest stage of life. A high rate can indicate problems involving healthcare access, maternal health, nutrition, infectious disease, sanitation, poverty or newborn services, although the statistic alone cannot identify the cause. A declining rate generally indicates improving survival conditions, but researchers need cause specific and age specific data to determine which changes produced the improvement.
Modern analysis therefore combines infant mortality with neonatal mortality, maternal mortality, low birthweight, premature birth, vaccination coverage, disease prevalence and healthcare access. Infant mortality remains a fundamental demographic and public health measure because it links individual survival with wider conditions in health systems, households and societies.
