Use of term reference infants in assessing the developmental outcome of extremely preterm infants: lessons learned in a multicenter study

Objective Extremely preterm (EP) impairment rates are likely underestimated using the Bayley III norm-based thresholds scores and may be better assessed relative to concurrent healthy term reference (TR) infants born in the same hospital. Study design Blinded, certified examiners in the Neonatal Research Network (NRN) evaluated EP survivors and a sample of healthy TR infants recruited near the 2-year assessment age. Results We assessed 1452 EP infants and 183 TR infants. TR-based thresholds showed higher overall EP impairment than Bayley norm-based thresholds (O.R. = 1.86; [95% CI 1.56–2.23], especially for severe impairment (36% vs. 24%; p ≤ 0.001). Difficulty recruiting TR patients at 2 years extended the study by 14 months and affected their demographics. Conclusion Impairment rates among EP infants appear to be substantially underestimated from Bayley III norms. These rates may be best assessed by comparison with healthy term infants followed with minimal attrition from birth in the same centers. ClinicalTrials.gov ID Term Reference (under the Generic Database Study): NCT00063063