Why the United States preterm birth rate is declining.

The preterm birth rate in the United States declined to 11.4% in 2013, the lowest level since 1997. Although the United States has one of the highest preterm birth rates in the developed world, we are improving this outcome and therefore improving the lives of thousands of infants. Demographic changes that may be responsible include a reduced teenage birth rate and fewer higher-order multiple births. Additionally, a public policy shift to prevent nonmedically indicated births at <39 weeks' gestation and smoking bans in several states have been associated with the reduced rate of preterm births. Last, interventions such as 17 hydroxyprogesterone caproate, vaginal progesterone, and the use of cerclage in selected populations probably are contributing to the reduction in preterm deliveries. However, a large portion of these births could still be prevented with greater access and implementation of our current interventions, the reduction of modifiable risk factors for preterm birth, and expanded reporting of outcomes and risk factors to facilitate research for both prevention and treatment.