Infant Mortality

Infant mortality refers to the death of a child before reaching one year of age and is a widely used indicator of population health and socio-economic development. The infant mortality rate (IMR) expresses the number of deaths of infants under one year per 1,000 live births. Closely related is the child mortality rate, or under-five mortality rate, which measures deaths of children up to five years of age. These measures illustrate disparities in health systems, living conditions and access to medical care across regions. Over time, global rates of infant and child mortality have declined significantly due to advances in medical science, improvements in sanitation and nutrition, and strengthened public health systems.

Definition and Measurement

Infant mortality is commonly assessed through the infant mortality rate, defined as the number of deaths of infants aged under one per 1,000 live births in a given year. This indicator enables comparison across countries and over time. The under-five mortality rate provides complementary data by including deaths up to the age of five. Both measures are essential for tracking progress towards international health goals, including the United Nations Millennium Development Goals (MDGs) and the Sustainable Development Goals (SDGs). Globally, IMR fell from approximately 65 deaths per 1,000 live births in 1950 to around 29 deaths per 1,000 in 2015. During the same period, the under-five mortality rate dropped from 225 per 1,000 to 45, reflecting major improvements in global child health.

Global Trends and Patterns

Significant differences in infant mortality exist between regions. Africa continues to display the highest regional IMR, with recorded levels around 68 deaths per 1,000 live births in comparative studies across 135 countries. The determinants behind these variations include education, life expectancy, health care access and economic development. In 1990, an estimated 8.8 million infants died globally, alongside 12.6 million deaths of children under five. By 2021, annual child deaths under five fell to around five million. Research indicates that more than 60 per cent of under-five deaths are preventable through low-cost interventions such as vaccinations, adequate nutrition, exclusive breastfeeding and improved sanitation. Analysis of global progress shows that more than two-thirds of countries are already meeting or are on track to meet the SDG target reducing child mortality by 2030.

Classification of Infant Mortality

Infant mortality may be categorised into distinct forms to aid analysis:

• Late fetal death: death occurring from 22 weeks of gestation to birth or death within the first week postpartum.
• Neonatal death: death occurring within the first 28 days of life. Neonatal deaths account for approximately 40–60 per cent of infant mortality in many developing countries and are often linked to inadequate access to maternal and newborn care.
• Post-neonatal death: death occurring between 29 days and one year of age. Key contributors include malnutrition, infectious diseases, congenital conditions, complications from pregnancy, sudden infant death syndrome (SIDS) and environmental hazards within the home.

Each category reflects different underlying causes and therefore requires targeted preventive strategies.

Causes and Contributing Factors

Direct causes of infant mortality differ from contributing factors, although both influence the risk of death. Approximately 86 per cent of infant deaths globally are attributed to infections, premature birth, complications during delivery, perinatal asphyxia and birth injuries. Many causes are highly preventable with accessible and affordable interventions. While 99 per cent of infant deaths occur in developing countries, the most rapid reductions often occur in nations that have already achieved comparatively low IMR levels, reflecting improvements in advanced neonatal care.
Environmental, social and behavioural factors strongly influence risk. Barriers such as limited access to medical resources, unsafe housing, poor sanitation, lack of clean water, low maternal education and weak political infrastructure elevate IMR. Behavioural factors include smoking during pregnancy, alcohol consumption, drug misuse and inadequate prenatal care. Low birth weight is a significant risk factor in countries such as the United States, arising from socioeconomic inequalities, maternal health conditions, environmental exposures and psychological stress.

Major Causes of Infant Mortality

Three leading causes consistently associated with infant mortality are conditions related to preterm birth, birth defects, and SIDS. Historical data from North Carolina indicate that prematurity accounted for 37.5 per cent of infant deaths between 1980 and 1984, followed by congenital anomalies at 17.4 per cent and SIDS at 12.9 per cent.

Premature Birth

Preterm birth (PTB) is defined as birth before 37 weeks of gestation, with further categories describing the severity: mild preterm (32–36 weeks), very preterm (28–31 weeks) and extremely preterm (below 28 weeks). Lower gestational age markedly increases the risk of death due to physiological immaturity. Between 1990 and 2010, PTB became the second leading cause of death among neonates and children under five worldwide. In 2010, preterm complications accounted for 1.15 million deaths, with the highest rates in sub-Saharan Africa and South Asia.
Survival outcomes differ drastically between regions. In high-income countries, survival for infants born before 28 weeks approaches 90 per cent. In contrast, low-income countries may see survival rates as low as 10 per cent due to limited neonatal care infrastructure.
Preterm births occur in three main subgroups: spontaneous preterm labour, premature rupture of membranes and medically induced preterm delivery. Medically induced PTB may be necessary when continuing the pregnancy poses severe risks. Significant risk factors for spontaneous PTB include extremes of maternal age, short spacing between pregnancies, multiple gestations, use of assisted reproductive technologies, history of PTB, maternal undernutrition, smoking, substance misuse, low socioeconomic status, late or absent prenatal care and infections such as bacterial vaginosis or periodontal disease.
Many deaths linked to prematurity arise from underdeveloped organ systems, including the respiratory system—leading to pulmonary hypoplasia, infant respiratory distress syndrome, bronchopulmonary dysplasia and apnoea. The gastrointestinal tract, skin, immune system, cardiovascular system and haematological systems also show functional immaturity in preterm infants. While the biological mechanisms behind PTB remain unclear, inflammation is associated with approximately 80 per cent of spontaneous preterm births.

Neonatal and Post-Neonatal Causes

Neonatal mortality often results from limited access to skilled birth attendants, inadequate antenatal and postnatal care, and absence of advanced medical facilities. Post-neonatal deaths largely stem from preventable conditions including malnutrition, diarrhoeal disease, pneumonia, measles and malaria. Environmental hazards such as unsafe drinking water, overcrowded living spaces and exposure to household smoke significantly elevate risk.

Prevention and Public Health Interventions

Many measures have proven effective in reducing infant mortality. These include:

• Improved prenatal and antenatal care, ensuring early identification of pregnancy-related complications.
• Access to skilled birth attendants and emergency obstetric services.
• Immunisation programmes, reducing the prevalence of deadly childhood infections.
• Exclusive breastfeeding, which strengthens immunity and provides essential nutrients.
• Nutrition support for mothers and infants to reduce low birth weight.
• Improved sanitation and access to safe drinking water, lowering infection rates.
• Maternal education initiatives, producing long-term improvements in household health practices.