Preterm birth: burden, trends and prevention

SIMON COUSENS: Babies are usually born after about 40 weeks of gestation, but some are born early– preterm births. While the cut-off for defining a preterm birth is somewhat arbitrary, the generally-accepted definition is a baby born before 37 completed weeks of pregnancy. Preterm babies are at increased risk of disability and death compared with babies born after 37 weeks, but the clinical picture varies dramatically with gestational age. Often the focus is on extremely preterm birth– babies born at less than 28 weeks gestation. They have the highest risk of disability and death. But these babies only comprise about 5% of all preterm births.

Another 10% of preterm babies are born between 28 and 32 weeks gestation, and many of these should survive without neonatal intensive care. However, the great majority of preterm babies, 84%, are born only a few weeks early. Yet in low-income countries, many of these babies still die from lack of simple care, such as support for feeding since they cannot suck and breastfeed easily, or from becoming cold, or getting infections. As already noted in this course, preterm birth is now the leading cause of child death, yet only recently has it started to attract global attention. In 2012, the first estimates of preterm birth were published for 195 countries.

Led by the London School of Hygiene & Tropical Medicine working with the World Health Organisation, these estimates were published in a Lancet paper and in a new report called “Born Too Soon.” This report received major media attention, a link to World Prematurity Day, and parents’ group actions, with, for example, Niagara Falls and the Empire State Building lit purple.

These estimates suggest that of the 135 million babies born in 2010, about 15 million, 11%, were born preterm. This map shows the estimated proportion of babies who were born preterm in each country of the world in 2010. The darker the colour, the higher the proportion of babies who were preterm. Looking at the map, it is immediately evident that high preterm birth rates are not randomly distributed but tend to cluster in poorer regions of the world, particularly in Sub-Saharan Africa and South Asia. In fact, of the 11 countries with preterm birth rates above 15%, 9 are in Africa.

The next map shows the number of babies born preterm in each country. Darker colours indicate larger numbers of preterm babies. The number of preterm babies in a country depends on two things– the proportion of babies who are born preterm and the total number of babies born in a country. So not surprisingly, countries with large populations and large numbers of births tend to have large numbers of preterm births. But although 60% of preterm births occur in South Asia and Sub-Saharan Africa, preterm birth is not just a problem for poorer countries.

The United States of America, one of the richest countries in the world, has a preterm birth rate of 12% and more than half a million preterm births each year. This puts it sixth in the world with respect to numbers of preterm births. Preterm birth is a global problem.

Is preterm birth increasing or decreasing? For many countries in the world, there are not sufficient data available to answer this question. For high-income countries for which there are good data available, the answer is that it depends. It depends on the country and on the period of time that you’re looking at. Between 2000 and 2010, Sweden and the Netherlands recorded the largest relative reductions in their preterm birth rates. But for many countries, there was no detectable change or preterm birth rates actually increased.

In the United States, which, as we have seen, has a very large number of preterm births each year, the preterm birth rate increased between about 1990 and 2004 but may now have levelled off or even begun to reduce. What can we do to reduce preterm birth rates? A modelling exercise, published in The Lancet in 2013, examined the potential impact of ensuring high coverage of five interventions to reduce preterm birth– smoking cessation, decreasing multiple births from Assisted Reproductive Technologies, cervical cerclage, prostaglandins, and decreasing non-medically indicated use of caesarean section. Depressingly, this exercise suggested that in the 39 high-income countries studied, these interventions would only reduce preterm births by about 5%.

There is, therefore, a really urgent need to develop interventions that will have a greater impact. Preventing preterm birth is the most obvious way to reduce the burden of preterm birth. While we need to do better at preventing preterm birth, our ability to do so is currently limited, as we saw in the previous slide. This is a major research gap. The management of preterm labour, care of women in preterm labour, also offers some scope for reducing the burden of preterm birth. For example, there is strong evidence for the efficacy of antenatal corticosteroids, but recently concerns have been raised about their use in some settings.

However, the biggest impact on the burden of preterm birth in high-income countries has come from improvements in the care of preterm babies, much of it technologically complex. Yet even simple care is lacking for most of the babies born preterm in low and middle-income settings. Many preterm babies die who would have survived if they had access to the care available in high-income settings. Even simple care of preterm babies could reduce this burden in low and middle-income countries where most preterm births occur, and shortly we will consider how to achieve this.