The NICHD Neonatal Research Network's Follow-Up study is a multi-center cohort in which surviving extremely low birth-weight infants born in participating network centers receive neurodevelopmental, neurosensory and functional assessments at 22-26 months corrected age (Infants born prior to July 1, 2012 were seen at 18-22 months corrected age). Data regarding pregnancy and neonatal outcome are collected prospectively. The goal is to identify potential maternal and neonatal risk factors that may affect infant neurodevelopment.