Migration and risk of intellectual disability with and without autism: A population-based cohort study.

Objective To investigate whether parental migration, parental region of origin, timing of child's birth in relation to maternal migration and parental reason for migration are associated with intellectual disability (ID) with and without autism. Methods We used a register-based cohort of all individuals aged 0-17 years in Stockholm County during 2001-2011. General estimating equation logistic model and additionally sibling comparison were used to calculate odds ratios (ORs) and 95% confidence intervals (CIs). The models were adjusted for child's sex and birth year and parental age at child's birth, and additionally for migrant-specific variables in the analyses including only children with migrant parent(s). Results Within the eligible sample of 670,098 individuals, 3781 (0.6%) had ID with autism, and 5076 (0.8%) had ID without autism. Compared with children with Swedish-born parents, children with both parents born abroad had an increased risk of ID with autism (OR = 1.6, CI 1.5-1.8) and ID without autism (OR = 1.9, CI 1.7-2.0). Among these children with both parents born abroad, it was protective of ID with autism when the child's birth occurred before and later than four years after maternal migration, which was replicated in the sibling comparison. The associations with both conditions were more pronounced with parental origin in regions comprising low- and middle-income countries and with reasons other than work or study. Conclusions Parental migration is associated with ID regardless of co-occurrence of autism. Our results indicate an association between environmental factors during pregnancy related to migration and offspring ID with autism, although further confirmative studies are needed.