Preterm birth refers to a delivery that occurs before 37 weeks gestation and, globally, is the leading cause of death in children under the age of five years. Worldwide, the rates vary between five to 18 per cent.1 The overall rate in Australia in 2014 was 8.6 per cent; however, 14 per cent of babies of Indigenous mothers were born preterm, compared to 8 per cent of babies of non-Indigenous mothers.2

Preterm birth is associated with perinatal mortality, admission to neonatal ICU, morbidity in the first weeks of life, long-term neurological disability and increased risk of chronic lung disease.

Significant associations have been found between preterm birth and social disadvantage (OR 1.27), previous preterm birth, pre-existing or gestational diabetes, current urogenital infections, alcohol consumption and smoking at first antenatal visit.3 These conditions are all affected by the social determinants of health, which will be reviewed below.

Social determinants of health

The social determinants of health are the conditions in which people are born, grow, live, work and age. These circumstances are shaped by the distribution of money, power and resources at global, national and local levels. The social determinants of health are mostly responsible for health inequities – the unfair and avoidable differences in health status seen within and between countries.4

Recent evidence has led to the identification of key social determinants of health and wellbeing allowing collection of datasets to inform and support development of health policy. These key determinants are summarised in Box 1.

Key social determinants of health and wellbeing

Socioeconomic position has historically been defined by factors such as education, occupation and income. People who experience a lower socioeconomic position are at higher risk of illness and poor health outcomes, as well as a shorter life span. (This is also known as the social gradient and the lower your position on the social gradient, the more likely you are to experience adverse health outcomes.)

Education leads to a better understanding of the steps necessary for health and a better understanding and navigation of the healthcare system when illness does occur. A higher level of education leads to a more secure occupation and stable, higher income level. A higher income subsequently allows greater access to services that can provide health benefits, such as more nutritious food and better housing.

Early life the foundations of adult health are laid down as early as during pregnancy and the early childhood periods. The physical and emotional development of children during the first few years of life have flow-on effects for their future wellbeing. Children from lower socioeconomic backgrounds are more likely to perform poorly at school, thus adversely affecting their opportunities for employment and stable income in the future.

Social exclusion occurs where people experience social disadvantage, opportunity, participation and skills. This may occur due to prejudice based on race, religion, gender, sexual orientation, poverty, unemployment and discrimination. Social exclusion can lead, and contribute, to worsening of illness.

Social capital describes the benefits from the links that connect people within and between social groups. Social connectedness can provide resilience against poor health through social support and can also help in more tangible ways with increased access to employment and economic support.

Employment job security increases health, job satisfaction and wellbeing, while the converse is true for unemployment. Unemployment also increases the risk of premature death. Other aspects of work such as, control over work hours, conditions and satisfaction, also have an impact on physical and mental health.

Housing and residential environment safe and affordable housing is associated with better health, which increases participation in work and education. However, it is also a two-way relationship where ill-health can lead to unsuitable housing through unemployment and income loss. A favourable residential environment includes access to transportation and healthy affordable food, as well as mixed land usage promoting social interaction and physical activity.


Social determinants and preterm birth

Poorer countries and regions with more social disadvantage have higher preterm birth rates. The global average of preterm birth rate in 2010 was 11.1 per cent.5 There is wide variation between countries. Rates range from about five per cent in several northern European countries, to 18 per cent in Malawi. The highest rates of preterm birth in the world occur in low-income countries.6 Not surprisingly, the lowest rates tend to occur in high-income countries.

However, high rates of preterm birth are also seen in many high-income countries, such as Australia. For example, in the Northern Territory (NT) the preterm birth rate is approximately seven per cent. In the Aboriginal population in the NT, the preterm birth rate is up to 14 per cent. Aboriginal and Torres Strait Islander people make up about 30 per cent of the NT population and more than 70 per cent live in regional and remote communities,7 where social disadvantage is more common.

Spontaneous preterm birth is multifactorial with the precise cause being unidentified in up to half of all cases. Risk factors for preterm birth include; history of preterm birth, young or advanced maternal age, short inter-pregnancy intervals, low maternal body-mass index, multiple pregnancy, pre-existing non-communicable disease, hypertensive disease, infections and smoking.8

About 25–30 per cent of preterm births follow preterm premature rupture of membranes (PPROM).9 The cause of membrane rupture in most cases is unknown, but asymptomatic infection is a frequent precursor and tobacco exposure also plays an important part.

All of these factors are more commonly seen in populations of disadvantage. Teenage pregnancies occur more frequently in lower socioeconomic populations and may be related to lower education rates, higher unemployment rates and less access to contraception. Body mass index and poor nutritional status is affected by education and income. Infections and chronic disease are more common in poorer populations. Smoking rates are higher in low socioeconomic populations. It remains a vicious cycle.

The way forward

There is still much work to do to reduce the preterm birth rates nationally and globally. However, there will be little to gain unless we address the root cause of the problem. Babies will continue to be born preterm if we do not address the basic health needs of the mothers growing them. Health status cannot be fixed without addressing the social determinants. Without quality housing, food security, transport, access to good healthcare, education, income and social standing, health in disadvantaged populations will not improve. And we will continue to see high rates of poor outcomes. Unfortunately, there is no quick fix.

‘Think of social determinants as the root-causes of health and disease. Imagine a bucket full of health. This bucket has a hole in the bottom and the health is dripping out (disease). We can mop up the floor below every hour, maybe even squeeze some of the health back into the bucket from the mop. But eventually, the health will be lost because we are not addressing the root of the problem. Instead, we can look for ways to prevent the hole and stop the leak from occurring.’ Alessandro R Demaio 2012.