Methods

Design: Population-based cohort study.

Setting: National register of children born in Denmark from 1996 to 2006.

Patients: 655 615 children with an estimated time of conception over 11 years to December 2006; 2644 children exposed to antiepileptic drugs during pregnancy and 508 exposed to valproate. Follow up to autism spectrum diagnosis; death; emigration; or until 31 December 2010. Excluded Those with likely errors or missing values for gestational age, adopted children, and death <1 year old.

Risk factors: Parental age at conception, parental psychiatric history, gestational age, birth weight, sex, congenital malformations and parity.

Outcomes: Absolute risk (cumulative incidence) and the HR of autism spectrum disorder and childhood autism in children after exposure to valproate in pregnancy.