Objective: To examine the impact of intrauterine as well as neonatal growth, prematurity, personal and environmental risk factors on intelligence in adulthood in survivors of the early neonatal intensive care era.
Methods: A large geographically based cohort comprised of 94 % of all individuals born alive in the Netherlands in 1983 with a gestational age below 32 weeks and/or a birth weight less than 1,500 gram (POPS-study). Intelligence was assessed in 596 participants at 19 years of age and was adjusted for nonresponsiveness using multiple imputation. Intrauterine and neonatal growth were assessed by weight, length and head circumference at birth and at 3 months of corrected age. Environmental and personal risk factors were: maternal age, education of the parent, sex and origin.
Results: The cohort’s mean IQ was 97.8 (SD 15.6). In multiple regression analysis, participants with high-educated parents had a 14.2 points higher IQ than those with low-educated parents. 1 SD increase in birth weight was associated with 2.6 points higher IQ and a 1-week increase in gestational age with a 1.3 points higher IQ. Persons born to young mothers (<25 yrs) had 2.7 points lower IQ and males had 2.1 points higher IQ than females. The effect on intelligence after early (symmetric) intrauterine growth retardation was more pronounced than after later (asymmetric) intrauterine or neonatal growth retardation. These differences in mean IQ remained when participants with overt handicaps were excluded.
Conclusion: Health factors such as prematurity, intrauterine and neonatal growth are of predictive value. The timing of growth retardation is important for later intelligence. Parental education however, best predicted later intelligence in very preterm or very low birth weight infants.
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