Infant mortality is the death of young children under the age of 1. This death toll is measured by the infant mortality rate (IMR), which is the number of deaths of children under one year of age per 1000 live births. The under-five mortality rate, which is referred to as the child mortality rate, is also an important statistic, considering the infant mortality rate focuses only on children under one year of age. Premature birth is the biggest contributor to the IMR. Other leading causes of infant mortality are birth asphyxia, pneumonia, congenital malformations, term birth complications such as abnormal presentation of the foetus umbilical cord prolapse, or prolonged labor, neonatal infection, diarrhoea, malaria, measles and malnutrition. One of the most common preventable causes of infant mortality is smoking during pregnancy. Many factors contribute to infant mortality, such as the mother's level of education, environmental conditions, and political and medical infrastructure. Improving sanitation, access to clean drinking water, immunization against infectious diseases, and other public health measures can help reduce high rates of infant mortality. In 1990 9 million infants younger than 1 year died globally.