ArticlesNational, regional, and worldwide estimates of preterm birth rates in the year 2010 with time trends since 1990 for selected countries: a systematic analysis and implications
Introduction
Preterm birth complications are estimated to be responsible for 35% of the world's 3·1 million annual neonatal deaths, and are now the second most common cause of death after pneumonia in children under 5 years old.1 Preterm birth also increases the risk of death due to other causes, especially from neonatal infections,2, 3 and in almost all high-income and middle-income countries, preterm birth is the leading cause of child deaths.1 Additional to its contribution to mortality, preterm birth has lifelong effects on neurodevelopmental functioning such as increased risk of cerebral palsy, impaired learning and visual disorders, and an increased risk of chronic disease in adulthood.4 The economic cost of preterm birth is high in terms of neonatal intensive care and ongoing health-care and educational needs. The social cost is also high, with many families experiencing the sudden loss of a preterm baby or a stressful hospital stay, sometimes for months.5
The WHO defines preterm birth as any birth before 37 completed weeks of gestation, or fewer than 259 days since the first day of the women's last menstrual period (LMP)6 and this can be further subdivided on the basis of gestational age: extremely preterm (<28 weeks), very preterm (28–<32 weeks), and moderate or late preterm (32–<37 completed weeks of gestation; figure 1). These subdivisions are important since decreasing gestational age is associated with increasing mortality, disability, intensity of neonatal care required, and hence increasing costs.
Preterm birth is a syndrome with a variety of causes which can be broadly classified into two groups: (1) spontaneous preterm birth and (2) provider-initiated preterm birth (defined as induction of labour or elective caesarean section before 37 completed weeks of gestation for maternal or fetal indications or other non-medical reasons, and sometimes previously called “iatrogenic”).7 Globally, the highest burden countries have very low levels of provider-initiated preterm births, with most African countries having caesarean sections rates lower than 5%.8 However, many high-income and middle-income countries have increasingly high numbers of provider-initiated preterm births and a recent assessment of 872 provider-initiated preterm births at 34–36 weeks' gestation in the USA suggested that more than half were done in the absence of a well defined medical indication.9
Spontaneous preterm birth is a multifactorial process, resulting from the interplay of factors causing the uterus to change from quiescence to active contractions and to birth before 37 completed weeks of gestation. The precursors vary by gestational age,10 with the precise cause of spontaneous preterm labour being unidentified in up to half of all cases.11 Individual or family history of preterm birth is a strong risk factor.12 Many other maternal factors have been associated with an increased risk of spontaneous preterm birth, including young or advanced maternal age, short interpregnancy intervals, low maternal body-mass index (BMI), multiple pregnancy, pre-existing non-communicable disease, hypertensive disease of pregnancy, and infections.13, 14
The number of liveborn preterm babies, whether singleton or multiple births, is the numerator for preterm birth rates. Liveborn preterm babies drive the need for neonatal care, and in high-income countries half of babies under 25 weeks now survive, but with increasing evidence of major disability.15 By contrast, in low-income and many middle-income settings, moderate and late preterm babies do not have even basic care and account for most preterm babies dying. However, from a public health perspective for policy and planning, and from a family loss perspective, both liveborn and stillborn babies born before term are important (figure 1).
The International Classification of Diseases: tenth revision (ICD-10) recommends recording all newborns with any signs of life at birth as livebirths.16 However, for extremely preterm babies, practice is variable and is closely linked to perceptions of viability and stillbirth registration thresholds. Classifications vary between countries and over time, complicating the comparison of reported rates and interpretation of time trends (figure 1).17, 18 Furthermore, some reports exclude babies with congenital abnormalities, and others include only singleton births. Additionally, methods for assessing gestational age have improved over time, at least in high-income countries, and variations in methods for measurement of gestational age further complicate the interpretation of preterm birth rates both within and between countries.
These differences and the absence of routinely collected data on preterm birth rates in many countries have limited the understanding of the size of the burden of preterm birth globally. A previous exercise estimated that 9·6% of livebirths worldwide in 2005 were preterm (12·9 million preterm births).19 No national systematic estimates of preterm birth rates have been published,20 and no multicountry time trend analysis is available.
In this study, we report worldwide, regional, and national estimates of preterm birth rates for 184 countries in 2010, and provide a quantitative assessment of the uncertainty surrounding these estimates. We have based the regional estimates on the Millennium Development Goal (MDG) regions (appendix p 1).21 We also present trend estimates for the period 1990–2010, where sufficient data exist. In the interests of public health planning, we also estimate preterm birth by three subgroups—namely, extremely preterm, very preterm, and moderate or late preterm (figure 1).
For the purpose of these estimates, the definition of the preterm birth rate used is “all livebirths before 37 completed weeks, whether singleton, twin, or higher order multiples, divided by all livebirths in the population”.
Section snippets
Data inputs
We assessed preterm birth data for inclusion from four sources: national registries or statistical offices, Reproductive Health Surveys,22 unpublished data from principal investigators collaborating with the Child Health Epidemiology Reference Group, and published papers identified through a systematic review (figure 2).
We systematically searched all the National Statistical Offices websites,24 and Ministry of Health websites. For countries without National Statistical Office or Ministry of
Results
Based on 184 countries, the global average preterm birth rate in 2010 was 11·1% (uncertainty range 9·1–13·4%), giving a worldwide total of 14·9 million (12·3–18·1 million; table 3). Preterm birth rates varied widely between countries (figure 3; appendix pp 65–72 and country plots for individual country data). At a national level, the estimated preterm birth rate ranged from about 5% in several northern European countries to 18% in Malawi. In 88 countries, this rate was lower than 10%. Of the 11
Discussion
We estimated national preterm birth rates for 184 countries in the year 2010 suggesting a worldwide total of 14·9 million preterm births (uncertainty range 12·3–18·1 million), more than one in ten of all babies (panel). Most preterm births (84%, 12·5 million) occur after 32 completed weeks of gestation. Most of these newborns would survive with supportive care, and without neonatal intensive care.28 Yet, a huge survival and equity gap remains between the richest and poorest countries.28
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