Preterm birth is one of the most difficult and critical obstetrical difficulties. Despite decades of study and therapeutic improvement, around one out of every ten infants in the United States is born prematurely. These babies are responsible for around three-quarters of prenatal death and more than half of long-term neonatal illness, at a substantial social and economic cost. Because preterm birth is the common endpoint for a number of pathophysiologic processes, comprehensive categorization methods for preterm birth phenotype and etiology have been suggested. In average, roughly one-half of preterm births are caused by spontaneous preterm labor, a quarter by premature prelabour rupture of membranes (PPROM), and the remaining quarter by purposeful preterm births caused by maternal or fetal problems. 

In the United States, there are significant racial differences in the preterm birth rate. The goal of this paper is to discuss the risk factors, screening tools, and therapies for avoiding spontaneous preterm delivery, as well as to examine the evidence supporting their therapeutic functions. This Practice Bulletin has been updated to incorporate information on rising preterm birth rates in the United States, inequalities in preterm birth rates, and methods to screening and preventive efforts for patients at risk of spontaneous preterm delivery.