Objective: To examine the effect of intrauterine and neonatal growth, prematurity and 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 94% of all babies born alive in the Netherlands in 1983 with a gestational age below 32 weeks and/or a birth weight >1500 g (POPS study). Intelligence was assessed in 596 participants at 19 years of age. Intrauterine and neonatal growth were assessed at birth and 3 months of corrected age. Environmental and personal risk factors were maternal age, education of the parent, sex and origin.
Results: The mean (SD) IQ of the cohort was 97.8 (15.6). In multiple regression analysis, participants with highly educated parents had a 14.2-point higher IQ than those with less well-educated parents. A 1 SD increase in birth weight was associated with a 2.6-point higher IQ, and a 1-week increase in gestational age was associated with a 1.3-point higher IQ. Participants born to young mothers (<25 years) had a 2.7-point lower IQ, and men had a 2.1-point higher IQ than women. 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.
Conclusions: Prematurity as well as the timing of growth retardation are important for later intelligence. Parental education, however, best predicted later intelligence in very preterm or very low birthweight infants.
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* Members of the Dutch Collaborative POPS-19 Study Group are listed in Acknowledgements.
Funding: The organisations mentioned in the acknowledgements that sponsored the study had no involvement in study design, data collection, analysis, interpretation of the data, or in the writing of the report. POPS-19 was supported by grants from the Netherlands Organization for Health Research and Development (ZonMw), Edgar Doncker Foundation, Foundation for Public Health Fundraising Campaigns, Phelps Foundation, Swart-van Essen Foundation, Foundation for Children’s Welfare Stamps, TNO Quality of Life, Netherlands Organization for Scientific Research (NWO), Dutch Kidney Foundation, Sophia Foundation for Medical Research, Stichting Astmabestrijding and the Royal Effatha Guyot group. The corresponding author had full access to all data in the study and had final responsibility for the decision to submit for publication
Competing interests: None.
Ethics approval: Institutional review boards in all centres gave approval.