Cerebral palsy and perinatal mortality in children born in Norway to immigrant mothers.

This was a registry study of births and diagnoses, not a trial or treatment study, so it can describe associations but cannot show that immigration status caused any difference. The authors adjusted for each listed risk factor one at a time, but they could not adjust for education, income, lifestyle factors such as body mass index and smoking, language spoken, fluency in Norwegian, time since immigration, or level of integration. Mothers born outside Norway were grouped by country income level, and the sample from each country was small, so the groups may not represent all people from those countries. Some risk factors may have happened after immigration, and it was unknown whether mothers born in Norway were second-generation immigrants. Some comparisons involved small numbers, especially severe hearing impairment among mothers from high-income countries and brain grey matter injury among mothers from low- or middle-income countries. Missing data were handled by using only cases with data, and the paper does not show how much missingness affected each analysis. Higher perinatal mortality among mothers from low- or middle-income countries could remove children who would otherwise have been diagnosed with cerebral palsy, which may partly explain lower cerebral palsy prevalence.

Do not read the lower cerebral palsy prevalence among children of immigrant mothers as proof that immigration protects against cerebral palsy. This was an observational registry study, and the authors suggest that higher perinatal mortality among mothers from low- or middle-income countries may reduce the number of children later diagnosed with cerebral palsy.