Review
The epidemiology, etiology, and costs of preterm birth

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Summary

After decades of rising preterm birth rates in the USA and other countries, recent prematurity rates seem to be on the decline. Despite this optimistic trend, preterm birth rates remain higher in the USA, where nearly one in every eight infants is born early, compared to other developed countries. The prevention of preterm birth is considered a public health priority because of the potential to reduce infant and childhood morbidity and mortality related to this condition. Unfortunately, progress has been modest. One of the greatest challenges in studying this outcome is that preterm birth is a complex condition resulting from multiple etiologic pathways. Recently, experts have developed innovative frameworks for classifying and studying preterm birth based on phenotype. These proposed classification systems have only recently been adopted, but a different perspective on a longstanding problem has the potential to lead to new discoveries.

Introduction

Preterm birth (PTB), defined as delivery prior to 37 weeks of gestation, is considered one of the leading health indicators of a nation [1], as it is the most frequent cause of neonatal death and the second most frequent cause of death in children aged <5 years worldwide [2]. Furthermore, those infants who do survive have higher rates of long-term morbidity, including neurologic and developmental disabilities, compared to infants born full term [3]. The development of effective preventive measures to reduce the incidence of PTB is, thus, urgently needed. This requires a thorough understanding of the epidemiology of the condition as well as familiarity with the previously studied factors thought to be related to pathogenesis. But perhaps most importantly, progressive approaches to studying this longstanding public health problem are essential.

Section snippets

Recent trends in preterm birth rates

During the latter part of the 20th century, an alarming increase in the PTB rate occurred in the USA as well as in other countries worldwide [4], [5]. Multiple factors were thought to have contributed to the rising PTB rate including higher average maternal age, more frequent use of assisted reproductive technologies, an increase in non-infertility-related multiple gestations (multiple gestation will be discussed elsewhere in this volume), and higher rates of preterm inductions and cesarean

Racial disparities in preterm birth

One of the most persistent findings in the study of the epidemiology of PTB is that rates of PTB vary according to women's racial and ethnic background. This disparity is most clearly evident in the relatively heterogeneous US population. In 2013, 16.3% of pregnant non-Hispanic black women delivered prior to 37 weeks compared to only 10.2% of non-Hispanic white women and 11.3% of Hispanic women. Additionally, the early PTB rate (<32 weeks) in non-Hispanic black women was more than twice the

Approaches to the study of the etiology of premature birth

Preterm birth is often regarded as a single outcome in clinical practice, public policy, and research. However, in reality, numerous biological mechanisms that vary between individuals are thought to lead to PTB. These etiologic pathways are poorly understood, despite significant research efforts. In contrast, there are multiple well-established risk factors for PTB, many of which are addressed in other chapters of this issue of Seminars (Box 1). The identification of risk factors by clinicians

The cost of prematurity

In 2005, it was estimated by the Institute of Medicine (IOM) that the societal cost of PTB in the USA annually was $26 billion [33]. This value included medical care costs up to age 5 years for children born preterm, maternal delivery costs, and the cost of early intervention. In addition, disability-specific lifetime medical, special education, and lost productivity costs for four specific developmental disabilities that are associated with PTB, including cerebral palsy, mental retardation,

Conclusion

Whereas the PTB rate is declining in many developed countries, currently about one in every eight infants in the USA is born prematurely. The consequences of PTB are substantial as it is associated with higher rates of infant morbidity and mortality, increased risk of long-term medical complications and neurodevelopmental impairment, family stress, and significant societal cost. The prevention of PTBs is a public health priority. However, research in the area of PTB prevention, although

Conflict of interest statement

None declared.

Funding sources

None.

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