Slower reaction times and impaired learning in young adults with birth weight <1500 g.

OBJECTIVE

Children with very low birth weight (VLBW; <1500 g) perform worse on cognitive tests than do children who are born at term. Whether this difference persists into adulthood has been little studied. We assessed core neurocognitive abilities (processing speed, working memory, attention, and learning capacity) in young adults with VLBW and in term-born control subjects.

METHODS

In conjunction with the Helsinki Study of Very Low Birth Weight Adults, 147 VLBW and 171 control subjects who were aged 18 to 27 years and did not have neurosensory impairments performed a computerized test battery (CogState Ltd, Melbourne, Australia). T tests and linear regression models were used. Cohen's d was used to express effect size (ES).

RESULTS

VLBW adults had slower reaction times than did control subjects on all 5 tasks: simple reaction time (mean difference: 4.0% [95% confidence interval (CI): 1.1%-7.0%]; ES: 0.30), choice reaction time (mean difference: 3.2% [95% CI: 0.3%-6.2%]; ES: 0.24), working memory (mean difference: 8.4% [95% CI: 3.7%-13.4%]; ES: 0.40), divided attention (mean difference: 7.2% [95% CI: 2.7%-11.9%]; ES: 0.36), and associated learning reaction time (mean difference: 6.4% [95% CI: 1.3%-11.9%]; ES: 0.28). In addition, VLBW adults showed impaired learning abilities on the associated learning task (percentage of correct responses: 85.7 vs 80.2; P < .001; ES: 0.64). The results were little affected by adjustment for confounders.

CONCLUSIONS

Nonimpaired VLBW individuals exhibited slower psychomotor speed and lower accuracy on the associated learning task. These results indicate that very preterm birth, even when obvious neurosensory deficits are absent, may have long-term consequences on core neurocognitive abilities.