The Prognosis of Preterm Infants Born at the Threshold of Viability: Fog Over the Gray Zone – Population-Based Studies of Extremely Preterm Infants

The limit of viability for premature newborns has changed in recent decades, but whether to initiate or withhold active care for periviable infants remains a subject of debate because the chances of survival and the extent of severe neurological impairment can be unclear. In our review, we analyzed large population-based studies of periviable infants from the past 2 decades. We compared survival rates and the incidence of early complications among survivors, including bronchopulmonary dysplasia, intraventricular hemorrhage, periventricular leukomalacia, retinopathy of prematurity, and necrotizing enterocolitis. Moreover, we assessed the perinatal factors that may affect the survival of preterm infants. We analyzed 15 studies reporting data on preterm infants born between 22 and 28 gestational weeks. None of these studies reported survival of an infant born before 22 gestational weeks. Survival rates of infants born at 24 weeks’ gestation were above 50% in most studies. The incidence of each complication was also higher among infants born at ≤24 weeks. Of the analyzed perinatal factors, antenatal corticosteroid therapy, birth weight, female sex, cesarean delivery, singleton pregnancy, and birth in a tertiary-level Neonatal Intensive Care Unit were found to be associated with improved survival in some studies. The different methodologies of the studies limited comparison of the results. Further investigations are needed to gain up-to-date information on the limit of viability, and standardized methods in future studies would enable more accurate comparisons of findings.