ABSTRACT
Approximately 5%–18% of babies are born preterm (i.e., before 37 weeks of completed gestation) worldwide. Prematurity affects about 7%–12% of births in developed countries.1 , 2 In the United Kingdom, an estimated 10% of infants are delivered prematurely and 12% in the United States.2 The World Health Organization divides preterm infants into three subcategories based on gestational age: extremely preterm infants born at <28 weeks; very preterm infants born at 28–31 weeks and 6 days gestation; and moderate to late preterm infants born at 32–37 weeks.1 In developed countries, prematurity is the leading cause of neonatal mortality, and preterm babies are at a greater overall risk of morbidity and long-term adverse outcomes than infants born at term.3 , 4 Extremely preterm infants are at highest risk; and the chances of survival without long-term sequelae increases with increasing gestation at birth.5 Advances in the care of extremely preterm infants over the last decades have increased rates of survival, and published data show improved outcomes for these infants. However, with medical advances, infants are surviving from much earlier gestations, and therefore, we still see poor outcomes with a high rate of long-term neurodevelopmental problems.5 – 7 The reasons why infants are born preterm vary. Some preterm infants are delivered spontaneously, while others are delivered early because obstetricians identify conditions that pose risks to the mother (e.g., preeclampsia) or fetus (e.g., growth restriction due to placental insufficiency). The proportion of preterm infants whose delivery is planned is greater in developed than in developing countries and has increased in developed countries over time. This is likely due to improved antenatal care identifying risks to the mother and the fetus, and also because the improved outcomes for preterm infants mean that early delivery is not now the “death sentence” that it once may have been.
