In a previous study, we found that infants transferred to a neonatal ward after delivery had an almost twofold increased risk of being diagnosed with infantile autism later in childhood in spite of extensive controlling of obstetric risk factors. We therefore decided to investigate other reasons for transfer to a neonatal ward, in particular hyperbilirubinaemia and neurological abnormalities.
We conducted a population-based matched case–control study of 473 children with autism and 473 matched controls born from 1990 to 1999 in Denmark. Cases were children reported with a diagnosis of infantile autism in the Danish Psychiatric Central Register. Conditional logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals [CI] and likelihood ratio tests were used to test for effect modification.
We found an almost fourfold risk for infantile autism in infants who had hyperbilirubinaemia after birth (OR 3.7 [95% CI 1.3, 10.5]). In stratified analysis, the association appeared limited to term infants (≥37 weeks gestation). A strong association was also observed between abnormal neurological signs after birth and infantile autism, especially hypertonicity (OR 6.7 [95% CI 1.5, 29.7]). No associations were found between infantile autism and low Apgar scores, acidosis or hypoglycaemia. Our findings suggest that hyperbilirubinaemia and neurological abnormalities in the neonatal period are important factors to consider when studying causes of infantile autism.