The Contribution of Mild and Moderate Preterm Birth to Infant Mortality

Abstract

The World Health Organization defines preterm birth as a gestational age at birth of less than 37 completed gestational weeks.¹ Preterm birth is recognized as a major public health problem by both clinicians and researchers because it is the leading cause of infant mortality in industrialized countries and also contributes to substantial neurocognitive, pulmonary, and ophthalmologic morbidity.^2-5 Caring for preterm infants also incurs large health care expenditures.⁶ Most studies of morbidity and mortality among preterm infants have focused on those born very preterm, ie, at gestational ages less than 32 weeks.^7-17 For infants born at 32 through 36 gestational weeks, the risks are much lower, especially with recent advances in neonatal intensive care.^7,16 On the other hand, from a public health perspective, births at gestational ages of 32 through 36 weeks are much more common than those at less than 32 gestational weeks.^7,18 Thus it is important to distinguish absolute risk both from relative risk (RR) and from public health impact (ie, etiologic fraction [EF]).