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Neurodevelopmental outcomes at 3 years old for infants with birth weights under 500 g. BACKGROUND: Marked improvements have been achieved in the survival of extremely low birth weight infants, but survival rates and prognoses of extremely small infants with birth weights ≤500 g remain poor. The aim of this study was to clarify long-term outcomes for surviving infants with birth weights ≤500 g. METHODS: The study population comprised fetuses of gestational age ≥22 weeks, expected live- or stillbirth weight ≤500 g, and birth date between 2003 and 2012. Developmental assessments were performed prospectively at 3 years old. RESULTS: Data were obtained for 21 fetuses, including 10 live births and 11 stillbirths. Of the 10 live births, median gestational age was 25.2 weeks (range, 22.4-27.1 weeks), median birth weight was 426 g (range, 370-483 g), and two neonates died before discharge. One infant with severe asphyxia died within 12 h and another infant with Down syndrome died at 34 days. The survival rate was thus 80%. All surviving infants were small for gestational age. Seven of the 8 surviving infants (88%) weighed less than 2500 g at a corrected age of 40 weeks. Seven infants were available for developmental assessments at 3 years old. One infant could not be followed. Two of those seven infants (29%) showed normal development, three infants (42%) showed mild neurodevelopmental disability, and two infants (29%) showed severe neurodevelopmental disability. One infant had periventricular leukomalacia and cerebral palsy. Two of the seven infants (29%) had short stature (<3 SD) at 3 years old. CONCLUSION: Although the survival rate among live births was good (80%) in this study, neurodevelopmental outcomes remained poor in infants with birth weights ≤500 g. Further large studies are needed to assess long-term outcomes for extremely small infants.