American Journal of Epidemiology Advance Access published online on November 17, 2007
American Journal of Epidemiology, doi:10.1093/aje/kwm291
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Original Contribution |
Variations in Prenatal Sociodemographic Factors associated with Intellectual Disability: A Study of the 20-Year Interval between Two Birth Cohorts in Northern Finland
1 Department of Public Health Science and General Practice, Faculty of Medicine, University of Oulu, Oulu, Finland
2 Department of Obstetrics and Gynecology, University Hospital of Oulu, Oulu, Finland
3 Department of Child Neurology, University Hospital of Oulu, Oulu, Finland
4 Clinic of Child Psychiatry, University Hospital of Oulu, Oulu, Finland
5 Hospital for Children and Adolescents, University Hospital of Helsinki, Helsinki, Finland
6 Department of Epidemiology and Public Health, School of Medicine, Imperial College London, London, United Kingdom
Correspondence to Dr. Marjo-Riitta Järvelin, Department of Epidemiology and Public Health, School of Medicine, Imperial College London, Norfolk Place, London W2 1PG, United Kingdom (e-mail: m.jarvelin{at}ic.ac.uk).
Received for publication October 23, 2006. Accepted for publication September 11, 2007.
The authors followed two cohorts of children born in northern Finland in 1966 (n = 12,058) and 1985–1986 (n = 9,432) to examine whether associations between maternal sociodemographic factors assessed during pregnancy and intellectual disability in the offspring changed over a 20-year interval. Both of the cohorts were followed up to the age of 11.5 years using similar methods and definitions of intellectual disability. Data on sociodemographic factors were based on comparable questionnaires returned by the mothers during the 25th week of gestation. Despite an interval of 20 years between the cohorts, the main indicators of socioeconomic disadvantage and maternal multiparity remained as having the largest impact on the incidence of intellectual disability, while single factors such as older maternal age at delivery, being single, and living in a remote area lost their association with intellectual disability. Over 20 years, prepregnancy maternal obesity (body mass index 
30) became a newly associated factor (adjusted odds ratio = 2.8, 95% confidence interval: 1.5, 5.3). A future challenge is to explore the mediating mechanisms between intellectual disability and its associated preventable intergenerational environmental or lifestyle factors.
cohort studies; demography; family characteristics; mental retardation; pregnancy; prenatal exposure delayed effects; social class
Abbreviations: CI, confidence interval; ID, intellectual disability; IQ, intelligence quotient; NFBC, Northern Finland Birth Cohort; OR, odds ratio