This prospective observational multicenter study was conducted at 6 academic perinatal centers from December 2012 to October 2015 (NCT01747863). Infants were screened if they were admitted to the NICU, ⩾ 36 weeks of gestation and had evidence of hypoxia–ischemia during the perinatal period. The later included a pH ⩽ 7.0 or a base deficit ⩾ 16 mmol l−1 in arterial or venous umbilical cord blood or any blood specimen during the 1st hour after birth. If the pH was 7.01 to 7.15, or base deficit 10 to 15.9 mmol per liter, or if a blood gas was not available, additional criteria were required. These included an acute obstetric event (for example, late or variable decelerations, cord prolapse, cord rupture, uterine rupture, maternal trauma, hemorrhage or cardiorespiratory arrest) and either a 10-min Apgar score ⩽ 5 or assisted ventilation initiated at birth and continued ⩾ 10 min. Infants who fulfilled these criteria underwent a standardized neurological examination at <6 h of age using the Sarnat score as modified by the Eunice Kennedy Shriver National Institute of Child Health and Human Development NICHD-NRN (Neonatal Research Network) trial of hypothermia.10 (link) The score evaluated six categories: level of consciousness, spontaneous activity, posture, tone, primitive reflexes (suck and Moro) and autonomic nervous system (pupils, heart rate and respiration). Each category was scored for pre-defined signs consistent with normal, mild, moderate or severe. Infants with ⩾ 1 abnormal category but no evidence of moderate or severe NE (defined as moderate and/or severe abnormality in three categories) were classified as mild NE. Exclusion criteria included a completely normal neurological exam, inability to enroll at ⩽ 6 h of life, presence of a major congenital abnormality or severe growth restriction (birth weight ⩽ 1800 g). The Institutional Review Board of each participating center approved the study and written informed consent was obtained from parents.