Late preterm birth.

In the United States, preterm birth rates continue to rise. Many reasons account for this increase, such as demographic changes, infertility treatments, increases in maternal age, more multiple gestations, increasing obesity rates, and maternal comorbid conditions. The American College of Obstetricians and Gynecologists suggests that preterm birth rates have also increased because of a dramatic rise in late preterm births, defined as births between 34 weeks and 36-6/7 weeks of gestation. Late preterm newborns are the fastest growing subset of neonates, accounting for approximately 74% of all preterm births and about 8% of total births. Reviewed is the current literature with regard to the growing problem of late preterm birth to provide the reader with a comprehensive overview of the burden of late preterm birth and to reassess the clinical opinion regarding timing of delivery.