Epidemiology of preterm birth.
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.