Comparison of the neurobehavioural profile of early-preterm infants against term and late-preterm infants using the Hammersmith neonatal neurological examination

Aim To compare the neurobehavioural profile of early-preterm infants (<32 weeks gestation) at term-corrected age (39(+0)-41(+6) weeks) versus late-preterm and full-term infants at similar term gestational ages. Methods Early-preterm infants were assessed neurologically at term-corrected age using the Hammersmith neonatal neurological examination. The raw scores of the 34 Hammersmith neonatal neurological examination items were converted to optimality scores. Pairwise comparison of neurobehavioural patterns between early-preterm infants at term-corrected age versus late-preterm and full-term infants at similar gestational ages were made using independent sample t tests. Differences in optimality scores between the three groups were evaluated using one-way analysis of variance. Results Sixty-eight early-preterm infants assessed at term-corrected age were compared against 75 late-preterm infants and 133 full-term infants. Mean total optimality scores (+/- standard deviation) of early-preterm, late-preterm and full-term infants at term-corrected age were 27.68 (+/- 3.97), 29.09 (+/- 2.45) and 31.58 (+/- 1.39), respectively (P < 0.001). The mean optimality score of early-preterm infants was significantly lower when compared pairwise with late-preterm infants and full-term infants with mean difference of -1.42 (P = 0.013) and -3.91 (P < 0.001), respectively. Conclusion The neurobehavioural profile of early-preterm infants lags significantly behind those of late-preterm and full-term infants at term-corrected age. This study also provides reference raw and optimality scores for all items in the Hammersmith neonatal neurological examination for early-preterm infants in a predominantly Asian population.