Elsevier

Seminars in Perinatology

Volume 41, Issue 7, November 2017, Pages 387-391
Seminars in Perinatology

Epidemiology of preterm birth

https://doi.org/10.1053/j.semperi.2017.07.009Get rights and content

Abstract

Preterm birth is a worldwide epidemic with a global incidence of 15 million per year. Though rates of preterm birth in the United States have declined over the last decade, nearly 1 in 10 babies is still born preterm. The incidence, gestational age, and underlying etiology of preterm birth is highly variable across different racial and ethnic groups and geographic boundaries. In this article, we review the epidemiology of preterm birth in the United States and globally, with a focus on temporal trends and racial, ethnic, and geographic disparities.

Introduction

Preterm birth, defined as delivery prior to 37 weeks gestational age, is a worldwide epidemic. The global incidence of preterm birth is approximately 15 million per year.1 In the United States, nearly 1 in 10 babies is born preterm. As the leading cause of neonatal morbidity and mortality, prematurity is not only an emotional burden for families but also an economic burden on society. The societal cost of prematurity in the United States—accounting for medical costs, educational costs, and lost productivity—has been estimated to be at least 26.2 billion dollars each year.2 Length of hospital stays for preterm infants average 13 days compared to 1.5 days for term infants, and medical costs for preterm infants in the first year of life average ten times greater than those for term infants ($32,325 compared to $3,325).

Section snippets

Preterm birth in the United States

The rate of preterm birth rose steadily in the United States in the late 20th century, from 9.5% in 1981 to a peak of 12.8% in 2006.3 Rates of preterm birth have fortunately declined over the last decade. The preterm birth rate reached a nadir of 9.57% in 2014. In 2015, however, the rate of preterm birth was 9.62%—up slightly from the year prior and representing the first time since 2006 that the United States saw an increase in the rate of preterm birth.4 It is intriguing to note, however,

Etiologies of preterm birth

Preterm birth can be further classified as spontaneous preterm birth or medically indicated (iatrogenic) preterm birth. Pathways to spontaneous preterm birth include preterm labor, preterm premature rupture of membranes, and second trimester spontaneous pregnancy loss. Approximately two-thirds of all preterm deliveries are spontaneous.3 Risk factors for spontaneous preterm birth include prior spontaneous preterm birth, short cervix, non-Hispanic black race, short inter-pregnancy interval,

Preterm birth disparities

While advances have been made in reducing the burden of prematurity, there are significant racial and ethnic disparities. Black race is an established risk factor for spontaneous preterm birth, and preterm birth rates in the United States are 48% higher among non-Hispanic black women compared to women of other racial groups.6 From 2012 to 2014, the average percentage of live births that were preterm was 8.5% for Asian/Pacific Islander women, 9.0% for white women, 9.1% for Hispanic women, 10.4%

Trends in U.S. preterm birth rates

Several authors have examined the temporal changes in preterm birth rates to further understand trends related to the gestational age and etiology of preterm deliveries. From 1990 to 2005, the preterm birth rate rose 20%, from 10.6% in 1990 to 12.7% in 2005. During this time period, the greatest increase in preterm deliveries based on gestational age was in the subgroup of late preterm birth which increased 25% from 7.3% in 1990 to 9.1% in 2005.10

Goldenberg et al.3 found that the increase in

Global trends

There is significant variation in the incidence of preterm birth worldwide. The rates of preterm birth in 184 countries in 2010 ranged from 5% in several Northern European countries to 18% in Malawi.15 Rates are highest in low income and lower-middle income countries (11.8% and 11.3% on average, respectively), whereas rates are lower in upper-middle and high-income countries (9.4% and 9.3%, respectively). More than 60% of all preterm births worldwide occur in low-resource, high-fertility

Our changing population

The population of childbearing women in the Unites States continues to evolve and influence the epidemiology of preterm birth. In 2015, the birth rate for women aged 35–39 was 51.7 births per 1000 women—a 13% increase since 2010. The birth rate for women aged 40–44 was 11.0 births per 1000 women—a 4% increase compared to 2014.4 Advancing maternal age, coupled with the United States obesity epidemic, means that pregnant women are more likely to have comorbidities that may necessitate an early

Goals for the future

The March of Dimes' goal is to reduce the incidence of preterm birth to 8.1% by the year 2020.19 In our efforts to move towards this goal, it is imperative that we continue to study the underlying mechanisms of preterm birth, develop targeted therapies, and work to eliminate disparities amongst at-risk women.

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