OBJECTIVE: To compare the accuracy of a prenatal outcomes calculator developed by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) with a postnatal neonatal intensive care unit (NICU) prediction model for mechanically ventilated infants. STUDY DESIGN: Over a 3-year period, we identified 89 ventilated infants born in our NICU between 23 and 25 weeks gestation. We retrospectively determined the predicted morbidity and mortality for each infant using the prenatal NICHD Neonatal Research Network: Extremely Preterm Birth Outcome Data website calculator. For our postnatal prediction model, we assessed 2 factors while each infant was on mechanical ventilation: daily intuitions about whether the infant would die before NICU discharge and abnormal head ultrasound. We compared the prenatal and postnatal models for predicting outcomes at 2 years adjusted age. RESULTS: Of the 89 infants, 54 (61%) died or had neurologic developmental impairment (NDI) and 35 (39%) survived without NDI. The NICHD Neonatal Research Network: Extremely Preterm Birth Outcome Data website calculator predicted that 61 (69%) would either die or have NDI and that 28 (31%) would survive without NDI. Positive clinicians' intuitions about survival combined with normal head ultrasound scan results during a trial of therapy in the NICU predicted a 30% greater chance for survival without NDI than the prenatal tool. CONCLUSIONS: When infants at the border of viability are born and cared for in the NICU, they move from predictions for population-based outcomes into predictions based on individual trajectories and outcomes. A clinical trial of therapy provides additional prognostic information that can guide parental decisions made near the time of birth.