Late preterm births: irreducible because E = mc2.

Am J Obstet Gynecol 204(6):459-60 (2011) PMID 21752750

Defined as delivery at 34(0/7)-36(6/7) weeks, late preterm births have increased by 15% between 1992 and 2002 and currently they occur in about 8% of singletons and 35% of multiple gestations. Compared with newborns at 39 weeks, late preterm births undeniably have a significantly higher rate of morbidity (respiratory distress syndrome, pneumonia, need for ventilation), as well as neonatal and infant mortality. Thus, to lower the rate of late preterm birth seems to be self-evident necessity, but there is a need for judicious caution because there is insufficient evidence that prolonging these pregnancies improves maternal-fetal outcomes.