Incidence, aetiology and neurodisability associated with severe microcephaly: a national surveillance study.

Objective: To determine the incidence, causes and neurodevelopmental impact of severe microcephaly (head circumference <-3SD) up to age 2 years.

Design: Binational active paediatric surveillance study undertaken in 2017-2018 to identify and characterise new diagnoses of severe microcephaly.

Setting: UK and Ireland.