Understanding the health of babies and expectant mothers

Progress on stillbirths and neonatal and infant mortality has slowed down in the UK in recent years. This explainer from Jessica Morris looks at the possible reasons why, and what can be done about it.

Explainer

Published: 06/11/2018

Rates of stillbirths, neonatal and infant mortality have been falling in the UK for over a century, as they have across most developed countries. However, over the last two decades rates have decreased more slowly than in other countries, and the latest data shows that in 2016 over 3,000 infants died before their first birthday.

What might be driving these trends in the UK and internationally? And what can the UK do to reduce its number of stillbirths and infant deaths? This explainer helps to answer these questions by drawing on internationally comparable data and looking at changes in the prevalence of risk factors over time in the UK.

How do stillbirth and infant mortality rates compare internationally?

Our 18 comparator countries were: Australia, Austria, Belgium, Canada, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Japan, Netherlands, New Zealand, Portugal, Spain, Sweden and the United States.

We compared the UK with 18 other high-income and industrialised countries, as in our jointly published report "How good is the NHS?"

Infant mortality rates (deaths under one year per 1,000 live births) have been gradually decreasing in all of the comparator countries over time. From 1994 onwards, the United States has consistently had the highest rate, with 5.6 infant deaths per 1,000 live births in 2016. In contrast, Finland had the lowest rate of 1.9. In 2016, the UK had the fourth highest infant mortality rate of the comparator countries, but the highest of comparable European countries.

The UK’s rate of infant mortality has remained at 3.9 deaths per 1,000 live births since 2013. Over the same period, rates have decreased in all other comparator countries except Denmark (where rates have increased) and Sweden (where rates have stalled but at a lower level of 2.4). If the UK had the same infant mortality rate as Finland in 2016, there would have been at least 1,500 fewer infant deaths.

International trends in infant mortality rates 06/11/2018

Chart

Source:  

UK – ONS, Vital statistics: population and health reference tables; All other countries – WHO, Global Health Observatory data repository

Read more

 

Neonatal mortality rates (deaths under 28 days per 1,000 live births) have also been declining internationally over time. Between 1990 and 2013, the rate of neonatal mortality in the UK dropped from 4.5 to 2.7 deaths per 1,000 live births. After this, however, rates have remained static, and even increased slightly to 2.8 deaths per 1,000 live births in 2016.

Japan consistently has the lowest neonatal mortality rate of the comparator countries (with 0.9 neonatal deaths per 1,000 live births in 2016), with the United States the highest (with 3.7 deaths per 1,000 live births). Based on this international data, the UK has the fifth highest neonatal mortality rate of the comparator countries. If the UK had the same neonatal mortality rate as Japan in 2016, there would have been at least 1,400 fewer neonatal deaths.

Some of the international variation in infant and neonatal mortality rates may be due to countries adopting different definitions of live birth. The World Health Organisation (WHO) defines a live birth as any infant born demonstrating independent signs of life, such as breathing, beating of the heart or voluntary movement. However, several countries apply a minimum threshold of a 22-week gestation period or a birth weight of 500 grams for babies to be registered as live births.

International trends in neonatal mortality rates 06/11/2018

Chart

Source:  

UK – ONS, Vital statistics: population and health reference tables; All other countries – WHO, Global Health Observatory data repository

Read more

The stillbirth rate in the UK fell to 4.4 stillbirths per 1,000 total births in 2015, and remained constant in 2016 [1]. This is the lowest rate since the early 1990s when the definition of a stillbirth was altered. The Still-birth (Definition) Act 1992 reduced the gestational age for stillbirth from 28 weeks to 24 weeks, to reflect improvements in survival rates of extremely premature infants. For this reason, international comparisons of stillbirth rates are difficult because some countries do not register deaths as stillbirths until later in pregnancy.

To enable international comparison, a recent study looked at stillbirth rates after 28 weeks’ gestation and found that in 2015, the UK’s stillbirth rate (2.9 per 1,000 births) was higher than in 10 of our comparator countries, including Germany (2.4), New Zealand (2.3) and Denmark (1.7). The stillbirth rate in the UK has also been falling more slowly than in other countries. Between 2000 and 2015, stillbirth rates declined by 22% in the UK. In contrast, Portugal – which had the same stillbirth rate as the UK in 2000 (3.7 per 1,000 births) – had a decrease of 41% over the same period.

A closer look at the UK

In 2016, there were 3,004 infant deaths (deaths under one year), 2,136 neonatal deaths (deaths under 28 days) and 3,430 stillbirths in the UK. As in most high-income countries, over 70% of infant deaths occurred in the neonatal period (first 28 days of life), and more than half occurred in the early neonatal period (first seven days of life).

Trends in stillbirth, infant and neonatal mortality rates in the UK 06/11/2018

Chart

Note:  

Stillbirths are per 1,000 live births and stillbirths (total births). Infant and neonatal mortality are per 1,000 live births

Source:  

ONS, Vital statistics: population and health reference tables

Read more

Rates of stillbirth, infant and neonatal mortality vary across the UK’s constituent countries. In 2016, the stillbirth rate in both England and Scotland was 4.3 per 1,000 total births, but reached 5.0 in Wales. The rate in Northern Ireland was lower at 3.4.

In contrast, the infant and neonatal mortality rates were lowest in Wales (3.1 infant deaths and 2.0 neonatal deaths per 1,000 live births), and highest in Northern Ireland (4.6 infant deaths and 3.5 neonatal deaths per 1,000 live births).

What are the causes and risk factors?

Infant deaths are subject to different causes and risk factors, depending on the age of the infant. Immaturity-related conditions, such as respiratory and cardiovascular disorders, were the most common cause of infant deaths in 2016 in England and Wales. 87% of these occurred in the neonatal period. Congenital anomalies were the second most common cause, accounting for the largest percentage (44%) of postneonatal deaths (deaths between 28 days and one year).

Over half (52%) of stillbirths in England and Wales in 2016 were unexplained. The remainder resulted from a lack of oxygen or trauma just before or during birth (19%), congenital anomalies (17%), other specific conditions (7%) and infections (2%).

Stillbirths and infant deaths are associated with a number of interrelating risk factors, some of which are modifiable. They include low birth weight, prematurity, maternal obesity, smoking in pregnancy, maternal age, and inequalities across different socioeconomic and ethnic groups.

How has the prevalence of risk factors changed over time?

Studying trends in risk factors for stillbirth and infant death could help to explain the UK’s stalling death rates in recent years, and the decline in its relative international position. Here we examine how the prevalence of some key risk factors have changed over time in the UK.

Preterm and low weight births

Prematurity (births before 37 weeks’ gestation) and low birth weight (under 2,500 grams) are major risk factors for stillbirth and infant death. A large proportion of babies will be born with a low birth weight because they were born prematurely, although some might be small for their gestational age. In 2015, seven out of 10 stillbirths and infant deaths in England and Wales were babies born prematurely. Almost half of all infant deaths occurred in babies born before 28 weeks of gestation (extremely preterm). Similarly, low birth weight babies accounted for two-thirds of stillbirths and around six out of 10 infant deaths.

What can increase your risk of having a premature or low birth weight baby? There are many factors, including multiple pregnancies (such as having twins or triplets), higher maternal age, smoking while pregnant, substance and alcohol misuse, poor maternal health and nutrition, and insufficient antenatal care. At a population level, a high proportion of low birth weight babies is primarily related to poorer antenatal maternal health.

Between 2006 and 2015, the proportion of preterm births in England and Wales has varied little, ranging from 7.1% to 7.6%. The fluctuations have mostly been due to a changes in the rate of moderate to late preterm births (32 to 37 weeks). The rates for extremely preterm (less than 28 weeks) and very preterm births (28 to 32 weeks) remained relatively constant. Data from the Euro-Peristat project shows that in 2010, rates of preterm births ranged from 5.5% to 15.7% across 29 European countries. The rates in England and Wales, Scotland and Northern Ireland were higher than in the Nordic countries, but lower than in Germany, Spain and Italy.

Trends in preterm births (England and Wales) 06/11/2018

Chart

Source:  

ONS, Infant mortality (birth cohort) tables in England and Wales

Read more

In the UK, the percentage of live births born weighing less than 2,500 grams decreased slightly from 7.5% in 2000 to 6.9% in 2016. The rate of low birth weight in the UK is about average against the comparator countries.

In general, there has been little change among all of the countries over the past 16 years. Greece and Japan consistently have the highest proportion of low birth weight babies, and Sweden and Finland have the lowest proportion. Had the UK reduced the proportion of babies born weighing less than 2,500 grams to the same percentage as Finland in 2016, there would have been around 20,000 fewer low birth weight babies.

International trends in low birth weight 06/11/2018

Chart

Source:  

WHO, Global Health Observatory data repository

Read more

Smoking in pregnancy

Smoking in pregnancy enables harmful chemicals (such as nicotine and carbon monoxide) to pass from the mother to the foetus. This reduces nutrient and oxygen availability, slowing foetal growth and development. Maternal smoking increases the risk of low birth weight and premature birth, which in turn increases the risk of infant mortality.

Babies born to women who smoke weigh, on average, 200 grams less than babies born to a non-smoker. Smoking in pregnancy is associated with a 47% increased risk of stillbirth, a 40% increased rate of infant mortality, and a two-fold increased risk of Sudden Infant Death Syndrome (SIDS). There is a dose-response relationship, as the risk of low birth weight, stillbirth and infant death increases with the number of cigarettes consumed.

In England, the proportion of mothers known to be smokers at the time of delivery fell from 15.8% in 2006/07 to 10.8% in 2017/18. Despite this, the reduction in smoking rates among pregnant women has slowed and stalled over the last couple of years, with a decrease of only 0.3% between 2015/16 and 2016/17 and an increase of 0.1% in 2017/18.

In addition, smoking in pregnancy is likely to be higher than the recorded rate, because the data is self-reported (smoking is often under-reported) and the rates do not include women who had a miscarriage or stillbirth (which are more common in women who smoke during pregnancy). International comparisons of rates of smoking in pregnancy are problematic due to variations in data collection. However, it appears that rates might be relatively high in the UK. The Euro-Peristat project reported that 12% of women in the UK smoked during pregnancy in 2010, compared with 8.5% of women in Germany and 4.9% in Sweden, for example.

Women’s smoking status at time of delivery (England) 06/11/2018

Chart

Source:  

NHS Digital, Statistics on Women’s Smoking Status at Time of Delivery: England

Read more

Maternal obesity

Being overweight (body mass index of 25 to 30 kg/m2) or obese (over 30 kg/m2) in pregnancy increases the risk of both stillbirths and infant deaths. Maternal obesity increases the risk of complications in pregnancy, including gestational hypertension (high blood pressure in pregnancy), gestational diabetes (diabetes in pregnancy) and pre-eclampsia (high blood pressure and protein in urine) – all of which increase the risk of stillbirth. Obesity also increases the risk of congenital abnormalities, premature birth and low birth weight, which are all risk factors for infant death.

Statistics on obesity in pregnancy have been routinely reported in England since 2015. Between April 2015 and July 2018, the proportion of women attending antenatal booking appointments who were overweight increased from 25.5% to 27.7%, and the proportion who were obese rose from 18.5% to 22%.

NICE guidelines recommend that obese women are helped to lose weight before they become pregnant, as dieting during pregnancy may harm the health of the unborn child. During pregnancy, NICE recommends that obese women should eat healthily and receive specific and practical advice about being physically active.

Proportion of women attending antenatal appointments who were obese (England) 06/11/2018

Chart

Source:  

NHS Digital, Maternity Services Monthly Statistics

Read more

Social inequality

Stillbirth and infant mortality rates in the most socioeconomically deprived areas of England are much higher than those in the least deprived. In 2016, the stillbirth rate was 5.5 per 1,000 total births in the most deprived areas, compared with 3.9 per 1,000 total births in the least deprived areas. For infant mortality, in the most deprived areas there were 5.9 infant deaths per 1,000 live births, whereas in the least deprived areas there were 2.6 per 1,000 live births.

Stillbirths and infant deaths by Index of Multiple Deprivation (England) 06/11/2018

Chart

Note:  

Stillbirths are per 1,000 live births and stillbirths (total births). Infant and neonatal mortality are per 1,000 live births

Source:  

ONS, Child mortality in England and Wales: 2016

Read more

Further to this, researchers have found that mortality rates have been rising for the poorest infants since 2010, but have continued to fall for more advantaged groups, meaning the inequality gap has widened. Infant mortality has been shown to be a strong indicator of the overall socioeconomic circumstances affecting children. Child poverty has risen in recent years, and the proportion of children in relative low income is expected to increase from 30% in 2015/16 to 37% in 2021/22 (based on incomes after housing costs). We could therefore expect to see further increases in infant mortality among the most disadvantaged families.

One reason why babies from deprived families have a greater risk of death is that women from poorer backgrounds have higher rates of smoking and obesity, and are more likely to book their antenatal appointment ‘late’ (after 13 weeks of completed pregnancy). Recent analysis from Public Health England shows that in the first six months of 2017, rates of maternal smoking in the most deprived decile were five times those in the least deprived decile. Furthermore, 38% of women living in the most deprived decile were overweight or obese, compared with 29% in the least deprived areas. And almost a quarter of women in the most deprived decile booked their antenatal appointment late, in comparison with only 13% of women in the least deprived areas.

However, there is also evidence to suggest that socioeconomic disadvantage may be an independent risk factor for infant and neonatal mortality. A study comparing child mortality in England and Sweden found that 3% of the excess risk of neonatal death and 11% of the excess risk of postneonatal death in England was explained by socioeconomic factors, independent of birth characteristics.

The UK has the second highest level of inequality of our comparator countries, as measured by the Gini coefficient (a measure of income or wealth distribution). In 2015, the Gini coefficient in the UK (0.36) was only exceeded by the United States (0.39), with Finland having the lowest level of inequality (0.26). The fact therefore that we have a more unequal society than most may be contributing to our relatively high infant and neonatal mortality rates.

In conclusion

This explainer has focused on some of the most important risk factors for stillbirths and infant and neonatal mortality. Some of the trends we have seen may help to explain why death rates have stalled in the UK in recent years, and why they have declined more slowly than in other comparable countries.

Prematurity and low birth weight are both strongly related to stillbirths and infant deaths, and in the UK there has been little change in either over the last few years. They in themselves are associated with smoking in pregnancy and maternal obesity, which are both modifiable factors. Although the proportion of mothers known to be smokers at the time of delivery has fallen since 2006, the decline in rates has stalled over the last couple of years. What is more worrying is the rise in the proportion of women attending antenatal appointments who are obese. Furthermore, mortality rates have risen for the most deprived infants but have fallen for the more advantaged groups, leading to a wider inequality gap.

There are also additional risk factors such as maternal age and ethnicity that may impact upon stillbirths and infant deaths. However, we chose not to focus on those here since they are not amenable to change.

In order for substantive changes to occur, improvements in the quality of care during pregnancy, labour and early infancy are needed, as well as reductions in the prevalence of risk factors, in order to bring the UK in line with other countries. Focusing on the factors relating to antenatal maternal health is most important, since the largest improvements in infant mortality could be achieved by reducing the prevalence of low birthweight and prematurity.

Given that the UK has greater inequality than most developed countries, it is especially important to prioritise policies that aim to eliminate smoking in pregnancy, reduce women’s obesity, and encourage expectant mothers to seek antenatal care as early as possible.

Footnote

  1. There is indication that stillbirth rates in the UK will continue to decline, as in 2017 there were 4.2 stillbirths per 1,000 total births in England and Wales.

References

Suggested citation

Morris J (2018), "Understanding the health of babies and expectant mothers", Nuffield Trust.

Comments