The preterm (less than 37 weeks of gestation) birth rate rose by more than 20 percent in the United States between 1990 and 2006 (1). Most of this increase was among infants born toward the end of the preterm period, at 34 to 36 full weeks of pregnancy, or during the period known as “late preterm” (1,2).
Although babies born before the 34th week of pregnancy are at the greatest risk of early death and life-long morbidity (3), it is becoming increasingly recognized that infants born late preterm are less healthy than infants born later in pregnancy (4–9). Late preterm babies are more likely than term babies to suffer complications at birth such as respiratory distress (4,9); to require intensive and prolonged hospitalization (4,8); to incur higher medical costs (5); to die within the first year of life (3,7,8); and to suffer brain injury that can result in long-term neurodevelopmental problems (6). Accordingly, increased high levels of late preterm births are an important public health issue.
