Methods
Study Population and Definitions
Liveborn infants enrolled in the Generic Database
registry of the NICHD Neonatal Research
Network were eligible for inclusion in the study
if they met the following three criteria: they were
born between January 1, 2000, and December 31,
2011, their gestational age at birth was 22 0/7 to
28 6/7 weeks, and they were born in a Neonatal
Research Network center.